In 1990 Walter Arfeuille of Belgium lifted a 281 5 kg object through a distance of 17 1 cm using only his teeth (a) How much work did Arfeuille do on the object J (b) What magnitude force did he exert on the object during the lift, assuming the force was constant kN 2 1 Points DETAILSSERCP11 5 1 P 003 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A cable exerts a constant upward tension of magnitude1 7010 4 N on a1 4010 3 kg elevator as it rises through a vertical distance of1 70m HINT (a) Find the work done by the tension force on the elevator (in J) J (b) Find the work done by the force of gravity on the elevator (in J) J 3 1 Points DETAILSSERCP11 5 1 P 007 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A tension force of155N inclined at35 0above the horizontal is used to pull a29 0kgpackingcrate a distance of6 10mon a rough surface If the crate moves at a constant speed, find (a) the work done by the tension force and (b) the coefficient of kinetic friction between the crate and surface HINT (a) the work done by the tension force (in J) J (b) the coefficient of kinetic friction between the crate and surface 4 1 Points DETAILSSERCP11 5 2 P 011 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A65 6kg runner has a speed of4 30m s at one instant during a long distance event HINT (a) What is the runner's kinetic energy at this instant (in J) J (b) How much net work (in J) is required todoublehis speed J 5 1 Points DETAILSSERCP11 5 2 P 014 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A59 0kg cheetah accelerates from rest to its top speed of31 5m s HINT (a) How much net work (in J) is required for the cheetah to reach its top speed J (b) One food Calorie equals 4186 J How many Calories of net work are required for the cheetah to reach its top speed Note Due to inefficiencies in converting chemical energy to mechanical energy, the amount calculated here is only a fraction of the energy that must be produced by the cheetah's body Cal 6 1 Points DETAILSSERCP11 5 5 P 021 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A block of mass2 60kg is placed against a horizontal spring of constant k 865N mand pushed so the spring compresses by0 0750m HINT (a) What is the elastic potential energy of the block spring system (in J) J (b) If the block is now released and the surface is frictionless, calculate the block's speed (in m s) after leaving the spring m s 7 1 Points DETAILSSERCP11 5 5 P 026 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Truck suspensions often have helper springs that engage at high loads One such arrangement is a leaf spring with a helper coil spring mounted on the axle, as shown in the figure below When the main leaf spring is compressed by distance y 0 , the helper spring engages and then helps to support any additional load Suppose the leaf spring constant is4 8010 5 N m,the helper spring constant is3 8010 5 N m,and y 0 0 500 m A side view of a truck suspension The truck body is above the wheel The main leaf spring spans the horizontal width of the wheel and is attached at both ends to the truck body The helper spring is aligned vertically with its lower end attached to the axle and the upper end unattached The upper end is a distance y 0 from the truck body (a) What is the compression of the leaf spring for a load of4 4010 5 N m (b) How much work is done in compressing the springs J 8 1 Points DETAILSSERCP11 5 5 P 030 MY NOTES ASK YOUR TEACHER A projectile of mass m is fired horizontally with an initial speed of v 0 from a height of h above a flat, desert surface Neglecting air friction, at the instant before the projectile hits the ground, find the following in terms of m , v 0 , h , and g (a) the work done by the force of gravity on the projectile W (b) the change in kinetic energy of the projectile since it was fired KE (c) the final kinetic energy of the projectile KE f (d) Are any of the answers changed if the initial angle is changed YesNo 9 1 Points DETAILSSERCP11 5 6 P 034 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A23 0cm long spring is hung vertically from a ceiling and stretches to31 5cm when an8 00kg mass is hung from its free end HINT (a) Find the spring constant (in N m) N m (b) Find the length of the spring (in cm) if the8 00kg weight is replaced with a175N weight cm 10 1 Points DETAILSSERCP11 5 6 P 038 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Two blocks are connected by a light string that passes over a frictionless pulley as in the figure below The system is released from rest while m 2 is on the floor and m 1 is a distance h above the floor Two objects are connected by a taught string passing over a pulley An object labeled m 2 rests on a table, and an object labeled m 1 dangles a distance h above the table (a) Assuming m 1 m 2 , find an expression for the speed of m 1 just as it reaches the floor (Use any variable or symbol stated above along with the following as necessary g ) v f (b) Taking m 1 7 0kg, m 2 4 1kg, and h 3 1m, evaluate your answer to part (a) m s (c) Find the speed of each block when m 1 has fallen a distance of1 4m m s 11 1 Points DETAILSSERCP11 5 6 P 043 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER The system shown in the figure below is used to lift an object of mass m 65 0kg A constant downward force of magnitude F is applied to the loose end of the rope such that the hanging object moves upward at constant speed Neglecting the masses of the rope and pulleys, find the following A hand pulls down with a downward force of vector F on a rope, which passes over a pulley attached to the ceiling The other end of the rope travels down and passes under a second pulley, then up to be attached to the ceiling An object labeled m hangs from the second pulley Three tensions are labeled as follows T 1 is next to the section of the rope that extends up from the second pulley to the ceiling T 2 is next to the rope that attaches the object to the second pulley T 3 is next to the rope that attaches the first pulley to the ceiling (a) Find the required value of F N (b) Find the tensions T 1 , T 2 , and T 3 ( T 3 indicates the tension in the rope which attaches the pulley to the ceiling ) T 1 N T 2 N T 3 N (c) Find the work done by the applied force in raising the object a distance of2 60m kJ 12 1 Points DETAILSSERCP11 5 7 P 051 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER What average mechanical power (in W) must a75 0kgmountain climber generate to climb to the summit of a hill of height405min50 0min Note Due to inefficiencies in converting chemical energy to mechanical energy, the amount calculated here is only a fraction of the power that must be produced by the climber's body HINT W 13 1 Points DETAILSSERCP11 5 7 P 055 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER Under normal conditions the human heart converts about12 8J of chemical energy per second into1 28W of mechanical power as it pumps blood throughout the body HINT (a) Determine the number of Calories required to power the heart for one day, given that 1 Calorie equals 4186 J Cal (b) Metabolizing 1 kg of fat can release about 9000 Calories of energy What mass of metabolized fat (in kg) would power the heart for one day kg 14 1 Points DETAILSSERCP11 5 8 P 059 MI MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER The force acting on a particle varies as in the figure below (The x axis is marked in increments of1 50m )A coordinate plane has a horizontal axis labeled x (m)and a vertical axis labeled F x (N) There are five points, connected by straight lines in order from A to E Point A is at (0,0) Point B is at (6,6) Point C is at (12,0) Point D is at (15,3) Point E is at (18,0) Find the work done by the force as the particle moves across the following distances (a) from x 0 m to x 12 0m J (b) from x 12 0m to x 18 0m J (c) from x 0 m to x 18 0m J 15 1 Points DETAILSSERCP11 5 A P 074 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A student evaluates a weight loss program by calculating the number of times he would need to climb a14 0mhigh flight of steps in order to lose one pound(0 45 kg)of fat Metabolizing1 00 kgof fat can release3 7710 7 Jof chemical energy and the body can convert about18 6 of this into mechanical energy (the rest goes into internal energy ) HINT (a) How much mechanical energy (in J) can the body produce from 0 450 kg of fat J (b) How many trips up the flight of steps are required for the90 0kg student to lose 0 450 kg of fat Ignore the relatively small amount of energy required to return down the stairs trips 16 1 Points DETAILSSERCP11 5 A P 078 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A hummingbird hovers by exerting a downward force on the air equal, on average, to its weight By Newton's third law, the air exerts an upward force of the same magnitude on the bird's wings Find the average mechanical power (in W) delivered by a2 60ghummingbird while hovering if its wings beat70 0times per second through a stroke3 42cmlong HINT W 17 1 Points DETAILSSERCP11 5 A P 081 MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER A truck travels uphill with constant velocity on a highway with a6 0slope A40 kg package sits on the floor of the back of the truck and does not slide, due to a static frictional force During an interval in which the truck travels300m, find the following (a) What is the net work done on the package J (b) What is the work done on the package by the force of gravity J (c) What is the work done on the package by the normal force J (d) What is the work done on the package by the friction force

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In 1990 Walter Arfeuille of Belgium lifted a 281.5-kg object through a distance of 17.1 cm using only his teeth.(a) How much work did Arfeuille

In 1990 Walter Arfeuille of Belgium lifted a 281.5-kg object through a distance of 17.1 cm using only his teeth.(a) How much work did Arfeuille do on the object? J (b) What magnitude force did he exert on the object during the lift, assuming the force was constant? kN

[-/1 Points]DETAILSSERCP11 5.1.P.003.

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A cable exerts a constant upward tension of magnitude1.7010⁴N on a1.4010³kg elevator as it rises through a vertical distance of1.70m.

HINT

(a)

Find the work done by the tension force on the elevator (in J).

(b)

Find the work done by the force of gravity on the elevator (in J).

[-/1 Points]DETAILSSERCP11 5.1.P.007.

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A tension force of155N inclined at35.0above the horizontal is used to pull a29.0kgpackingcrate a distance of6.10mon a rough surface. If the crate moves at a constant speed, find (a) the work done by the tension force and (b) the coefficient of kinetic friction between the crate and surface.

HINT

(a)

the work done by the tension force (in J)

(b)

the coefficient of kinetic friction between the crate and surface

[-/1 Points]DETAILSSERCP11 5.2.P.011.

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A65.6kg runner has a speed of4.30m/s at one instant during a long-distance event.

HINT

(a)

What is the runner's kinetic energy at this instant (in J)?

(b)

How much net work (in J) is required todoublehis speed?

[-/1 Points]DETAILSSERCP11 5.2.P.014.

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A59.0kg cheetah accelerates from rest to its top speed of31.5m/s.

HINT

(a)

How much net work (in J) is required for the cheetah to reach its top speed?

(b)

One food Calorie equals 4186 J. How many Calories of net work are required for the cheetah to reach its top speed? Note: Due to inefficiencies in converting chemical energy to mechanical energy, the amount calculated here is only a fraction of the energy that must be produced by the cheetah's body.

Cal

[-/1 Points]DETAILSSERCP11 5.5.P.021.

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A block of mass2.60kg is placed against a horizontal spring of constantk=865N/mand pushed so the spring compresses by0.0750m.

HINT

(a)

What is the elastic potential energy of the block-spring system (in J)?

(b)

If the block is now released and the surface is frictionless, calculate the block's speed (in m/s) after leaving the spring.

m/s

[-/1 Points]DETAILSSERCP11 5.5.P.026.

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Truck suspensions often have "helper springs" that engage at high loads. One such arrangement is a leaf spring with a helper coil spring mounted on the axle, as shown in the figure below. When the main leaf spring is compressed by distancey₀, the helper spring engages and then helps to support any additional load. Suppose the leaf spring constant is4.8010⁵N/m,the helper spring constant is3.8010⁵N/m,and

y₀= 0.500 m.

A side view of a truck suspension. The truck body is above the wheel. The main leaf spring spans the horizontal width of the wheel and is attached at both ends to the truck body. The "helper" spring is aligned vertically with its lower end attached to the axle and the upper end unattached. The upper end is a distancey₀from the truck body.

(a) What is the compression of the leaf spring for a load of4.4010⁵N? m (b) How much work is done in compressing the springs? J

[-/1 Points]DETAILSSERCP11 5.5.P.030.

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A projectile of massmis fired horizontally with an initial speed ofv₀from a height ofhabove a flat, desert surface. Neglecting air friction, at the instant before the projectile hits the ground, find the following in terms ofm,v₀,h, andg.(a) the work done by the force of gravity on the projectile

(b) the change in kinetic energy of the projectile since it was fired

KE=

KE_f=

(d) Are any of the answers changed if the initial angle is changed? YesNo

[-/1 Points]DETAILSSERCP11 5.6.P.034.

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A23.0cm long spring is hung vertically from a ceiling and stretches to31.5cm when an8.00kg mass is hung from its free end.

HINT

(a)

Find the spring constant (in N/m).

N/m

(b)

Find the length of the spring (in cm) if the8.00kg weight is replaced with a175N weight.

10.

[-/1 Points]DETAILSSERCP11 5.6.P.038.

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Two blocks are connected by a light string that passes over a frictionless pulley as in the figure below. The system is released from rest while

m₂

is on the floor and

m₁

is a distancehabove the floor.Two objects are connected by a taught string passing over a pulley. An object labeledm₂rests on a table, and an object labeledm₁dangles a distancehabove the table.

(a) Assuming

m₁>m₂,

find an expression for the speed of

m₁

just as it reaches the floor. (Use any variable or symbol stated above along with the following as necessary:g.)

v_f=

(b) Taking

m₁=7.0kg,

m₂=4.1kg,

and

h=3.1m,

evaluate your answer to part (a). m/s (c) Find the speed of each block when

m₁

has fallen a distance of1.4m. m/s

11.

[-/1 Points]DETAILSSERCP11 5.6.P.043.

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The system shown in the figure below is used to lift an object of mass

m=65.0kg.

A constant downward force of magnitudeFis applied to the loose end of the rope such that the hanging object moves upward at constant speed. Neglecting the masses of the rope and pulleys, find the following.A hand pulls down with a downward force of vectorFon a rope, which passes over a pulley attached to the ceiling. The other end of the rope travels down and passes under a second pulley, then up to be attached to the ceiling. An object labeledmhangs from the second pulley. Three tensions are labeled as follows.

T₁is next to the section of the rope that extends up from the second pulley to the ceiling.
T₂is next to the rope that attaches the object to the second pulley.
T₃is next to the rope that attaches the first pulley to the ceiling.

(a) Find the required value ofF. N (b) Find the tensionsT₁,T₂, andT₃. (T₃indicates the tension in the rope which attaches the pulley to the ceiling.)

T₁	=	N
T₂	=	N
T₃	=	N

12.

[-/1 Points]DETAILSSERCP11 5.7.P.051.

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What average mechanical power (in W) must a75.0kgmountain climber generate to climb to the summit of a hill of height405min50.0min?Note: Due to inefficiencies in converting chemical energy to mechanical energy, the amount calculated here is only a fraction of the power that must be produced by the climber's body.

HINT

13.

[-/1 Points]DETAILSSERCP11 5.7.P.055.

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Under normal conditions the human heart converts about12.8J of chemical energy per second into1.28W of mechanical power as it pumps blood throughout the body.

HINT

(a)

Determine the number of Calories required to power the heart for one day, given that 1 Calorie equals 4186 J.

Cal

(b)

Metabolizing 1 kg of fat can release about 9000 Calories of energy. What mass of metabolized fat (in kg) would power the heart for one day?

14.

[-/1 Points]DETAILSSERCP11 5.8.P.059.MI.

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The force acting on a particle varies as in the figure below. (Thexaxis is marked in increments of1.50m.)A coordinate plane has a horizontal axis labeledx(m)and a vertical axis labeledF_x(N). There are five points, connected by straight lines in order from A to E.

Point A is at (0,0).
Point B is at (6,6).
Point C is at (12,0).
Point D is at (15,3).
Point E is at (18,0).

Find the work done by the force as the particle moves across the following distances.(a) from

x= 0 m

x=12.0m

J (b) from

x=12.0m

x=18.0m

J (c) from

x= 0 m

x=18.0m

15.

[-/1 Points]DETAILSSERCP11 5.A.P.074.

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A student evaluates a weight loss program by calculating the number of times he would need to climb a14.0mhigh flight of steps in order to lose one pound(0.45 kg)of fat. Metabolizing1.00 kgof fat can release3.7710⁷Jof chemical energy and the body can convert about18.6% of this into mechanical energy (the rest goes into internal energy.)

HINT

(a)

How much mechanical energy (in J) can the body produce from 0.450 kg of fat?

(b)

How many trips up the flight of steps are required for the90.0kg student to lose 0.450 kg of fat? Ignore the relatively small amount of energy required to return down the stairs.

trips

16.

[-/1 Points]DETAILSSERCP11 5.A.P.078.

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A hummingbird hovers by exerting a downward force on the air equal, on average, to its weight. By Newton's third law, the air exerts an upward force of the same magnitude on the bird's wings. Find the average mechanical power (in W) delivered by a2.60ghummingbird while hovering if its wings beat70.0times per second through a stroke3.42cmlong.

HINT

17.

[-/1 Points]DETAILSSERCP11 5.A.P.081.

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A truck travels uphill with constant velocity on a highway with a6.0slope. A40-kg package sits on the floor of the back of the truck and does not slide, due to a static frictional force. During an interval in which the truck travels300m, find the following.(a) What is the net work done on the package? J (b) What is the work done on the package by the force of gravity? J (c) What is the work done on the package by the normal force? J (d) What is the work done on the package by the friction force?