Exercises the mass is 1. A rope is attached to a 2.0 kg rock and pulled. Write a net force equation if a) accelerating up b) accelerating down ( T - mg = ma) mg - T = ma) c) Find the cord tension if the mass is accelerating at i) 0.0 m/s2 ii) 1.0 m/s2 UP (20. N) iii) 2.0 m/s2 DOWN ( 22 N) iv) 9.8 m/s2 DOWN (16 N) (0.0 N) T 2 kg Fg 2. Find the acceleration of the mass if the cord tension is a) 30. N b) 19.6 N c) 9.6 N string 2 kg (5.2 m/s2 up; 0.0m/s2; 5.0 m/s2 down) 3. In the diagrams below, assume the force F is the only horizontal force on the block. If the first block accelerates at rate a, then find an expression for the unknown acceleration. (a/2,2a) acceleration = ? acceleration = a F 2M F M frictionless surface acceleration = a acceleration = ? 2F F M M"""""" Exercises 1. A 25.0 kg child ' Mo on a bathroo ' . i a .. m scale which reads in k . T reads 32.0 kg. Des ii)\": the motion of the child. g he Scale 3 stand (2.74 m/s2 acceleration up) 2. A person stands in an clev a) elevator at rest b) elevator accelerates up c) elevator moves up at constant speed d) elevator moves down at constant speed e) elevator accelerates down (F N=mg: FNmg=ma; FN=mg; FN=mg; mg-FN=ma) ator. Write a net force equation in each case 3. A 55.0 kg student is in an elevator accelerating up at 2.50 m/s2 . a) write a net force equation (FN-mg=ma) b) what would a force scale placed under their feet read? (676 N) 4. A 25 kg mass is falling and accelerating downwards a) write a force equation - (mg-Fair = ma; 65 N) b) What is the force of air resistance if the acc'n is 7.2 m/s2 DOWN 5. a) A 5.00 kg rock is. moving upwards on the earth and it experiences 5.00 N of air drag. Find its acceleration. b) A 5.00 kg rock is moving downwards on the earth and it experiences 5.00 N of air drag. Find its acceleration. c) The same rock is thrown downwards on the moon. Find its acceleration. (10.8 m/s2 down; 8.8 m/s2 down; 1.6 m/s2 down.... no air on moon!) 6. Find the acceleration if the applied force is a) 5 N (0.5 m/sz LEFT) b) 10 N (0 m/sz) c) 20 N (1 m/s2 right) > applied Force ION 10 kg rock friction 7. A 200. kg spaceship speeds up from rest to 250. m/s in 0.200 seconds. Assume there is no air friction and find 2 a) the acceleration using kinematics (1250 m/s ) b) the force from the engines (2.50x 105 N) E: 8. A 250. gram ball is moving to the left at stops it in 0.320 seconds. Find the horizontal ball by the person's hand. the i0 Physics 12 Student Workbook Donald J. Mathewson 2002 25.0 m/s. A person catches it and force and direction exerted on the 87 9. A 55.0 kg parachutist is falling at constant speed. What force of air resistance acts on the person? (539 N up) 10. A 10. kg mass (initially at rest) is pulled with a force of 30. N across a 8.0 m long rough surface. The force of friction from the surface is 10. N. a) given that the mass accelerates right, write a net force equation b) Find the acceleration of the mass. c) find the final speed of the mass (T-Ff=ma; 2.0m/s2:5.6 m/s) rope 10 kg rough surfacedown, compare the forces 1.11:\". up. w. u... --__-, (mg>T : mg- T = ma) T Fe 7. Find the weight of a 80.0 kg person a) on the Earth b) on the Moon c) 2000. km above the surface of the Earth, where g: 5.70 N/ kg (784 N; 128 N; 456 N) 8. An object in freefall experiences only the force of gravity. for such an object a) draw a force diagram b) write a net force equation (mg = ma) c) solve for the acceleration (a= g) 9. A 75 kg mountain climber free-falls for 10.0 m his safety rope. The rope stretches and stops the c egins to stretch (14.0 m/s) a) find the speed of the climb 'on for the 'slow down' by the rope (Tmg = ma) b) write a net force equati c) find the force from the rope (1580 N) 10. Add the force vectors to find the net force and direction: 6250 N North and 3500. N. 30.0\" S of West Physics 12 Student Workbook Dona1d J. Mathewson 2002 2. 3, 8 Exercises 1. A force of 400. N is required to start a box moving across the floor (so friction must be about 400 N). If the box has mass 40.0 kg, find the friction coefficient (1.02) 2. A 20.kg box sits on a floor with u=0.30 . What force is required to move the box across the floor a) at steady speed (58.8 N ) b) accelerating at 1 m/s2 (78.8 N) 3. A mass of 125 kg is being pulled to the right across a rough floor with an applied force of 200. N. Find the coefficient of friction if the acceleration of the mass is a) 0.0 m/s2 (0.163) b) 1.50 m/s2 right/speeding up (0.0102) c) 2.20 m/s2 left/slowing down (0.388) 4. Find the acceleration of a 100. kg dragster if its tires have u=0.80. (7.8 m/s2) 5. A 50.0 kg rollerblader moving at 3.00m/s drags a foot on the ground to stop. If u= 0.300, how far does the rollerblader go before stopping? (1.53 m) 6. A car is moving at speed v on a road with friction coefficient u. Show that the stopping distance is given by d = 2 Zug 7. A 10. kg box sits on a floor with us=0.25 and uk=0.20. Find the acceleration if the box is pulled with a) 15 N b) 22 N c) 30. N ( Om/s2; 0 m/s2; 1.0 m/s2) 8. . A 50.0 kg block is pushed with a force of 60.0 N across a 20.0 metre long floor. The first 10.0 metres of the floor are frictionless, but the last 10.0 metres have u=0.350. Describe the motion of the block (4.90 m/s after 10m, then goes 5.38 m further and stops) 9. A 50.0 kg person falling at 8.00 m/s hits the floor and stops in 0.0500 seconds. Find the force that the floor exerts on this person. (8490 N) 10. A 55.0 kg person stands on a newton scale. Find the scale reading in each case a) elevator at rest b) elevator accelerates up at 1.00m/s2 c) elevator moves up at constant speed d) elevator accelerates down at 1.00 m/s2 e) elevator accelerates down at 9.80 m/s2 (free fall) (539N; 594 N; 539 N; 484 N; ON ) 1 1. Find the speed when this projectile hits the ground (17.9 m/s) 5.00 m/s 15.0 m 95 Physics 12 Student Workbook Donald J. Mathewson 2002