PY 205 C2H3

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1. [-/2 Points] DETAILS (a) A runner starts from rest and in 2 s reaches a speed of 8 m/s. If we assume that the speed changed at a constant rate (constant net force), what was the average speed during this 2 s interval? average speed = m/s (b) How far did the runner go in this 2 s interval? distance = m (c) The driver of a car traveling at a speed of 22 m/s slams on the brakes and comes to a stop in 5 s. If we assume that the speed changed at a constant rate (constant net force), what was the average speed during this 5 s interval? average speed = m/s (d) How far did the car go in this 5 s interval? distance = m2. [-/2 Points] DETAILS MY NOTES On a straight road with the +x axis chosen to point in the direction of motion, you drive for 2 hours at a constant 20 miles per hour, then in a few seconds you speed up to 70 miles per hour and drive at this speed for 1 hour. (a) What was the x component of average velocity for the 3-hour period, using the fundamental definition of average velocity, which is the displacement divided by the time interval? Vavg,x= miles per hour 2 (b) Suppose instead you use the formula Vavg,x = _XXX. What do you calculate for the x component of average velocity? Vavg,x = - - Vix + VFX - miles per hour (c) Why does the formula used in 2 part (b) give the wrong answer? O That formula only applies at high speeds. O That formula isn't valid unless vy changes at a constant rate (constant force). That formula can only be used for projectile motion, such as a baseball that has been hit. Additional Materials WeBook3. [-/1.5 Points] DETAILS MY NOTES A cart rolls with low friction on a track. A fan is mounted on the cart, and when the fan is turned on, there is a constant force acting on the cart. Three different experiments are performed: (a) Fan off: The cart is originally at rest. You give it a brief push, and it coasts a long distance along the track in the +x direction, slowly coming to a stop. (b) Fan forward: The fan is turned on, and you hold the cart stationary. You then take your hand away, and the cart moves forward, in the +x direction. After traveling a long distance along the track, you quickly stop and hold the cart. (c) Fan backward: The fan is turned on facing the "wrong" way, and you hold the cart stationary. You give it a brief push, and the cart moves forward, in the +x direction, slowing down and then turning around, returning to the starting position, where you quickly stop and hold the cart. The figure displays four graphs of py (numbered 1-4), the x component of momentum, vs. time. The graphs start when the cart is at rest, and end when the cart is again at rest. Match the experiment with the correct graph. fan off ---Select--- fan forward ---Select--- fan backward ---Select--- # Additional Materials WeBookA cart rolls with low friction on a track. A fan is mounted on the cart, and when the fan is turned on, there is a constant force acting on the cart. Three different experiments are performed: (a) Fan off: The cart is originally at rest. You give it a brief push, and it coasts a long distance along the track in the +x direction, slowly coming to a stop. (b) Fan forward: The fan is turned on, and you hold the cart stationary. You then take your hand away, and the cart moves forward, in the +x direction. After traveling a long distance along the track, you quickly stop and hold the cart. (c) Fan backward: The fan is turned on facing the "wrong" way, and you hold the cart stationary. You give it a brief push, and the cart moves forward, in the +x direction, slowing down and then turning around, returning to the starting position, where you quickly stop and hold the cart. The figure displays four graphs of Fret, x the x component of the net force acting on the cart, vs. time. The graphs start when the cart is at rest, and end when the cart is again at rest. Match the experiment with the correct graph. fan off ---Select--- ! fan forward --Select--- fan backward ---Select--- ITA cart rolls with low friction on a track. A fan is mounted on the cart, and when the fan is turned on, there is a constant force acting on the cart. Three different experiments are performed: (a) Fan off: The cart is originally at rest. You give it a brief push, and it coasts a long distance along the track in the +x direction, slowly coming to a stop. (b) Fan forward: The fan is turned on, and you hold the cart stationary. You then take your hand away, and the cart moves forward, in the +x direction. After traveling a long distance along the track, you quickly stop and hold the cart. (c) Fan backward: The fan is turned on facing the "wrong" way, and you hold the cart stationary. You give it a brief push, and the cart moves forward, in the +x direction, slowing down and then turning around, returning to the starting position, where you quickly stop and hold the cart. The figure displays graphs of x, position along the track, vs. time. The graphs start when the cart is at rest, and end when the cart is again at rest. Match the experiment with the correct graph. Match to the graphs of x vs t Fan off: [---Select-- # Fan forward: [ -Select- Fan backward: ---Select---A ball of mass 0.7 kg flies through the air at low speed, so that air resistance is negligible. What is the net force acting on the ball while it is in motion? Fnet = N Which components of the ball's momentum will be changed by this force? --Select--- # What happens to the x component of the ball's momentum during its flight? --Select-- What happens to the y component of the ball's momentum during its flight? --Select-- What happens to the z component of the ball's momentum during its flight? ---Select--- ........ In this situation, why is it legitimate to use the formula for average y component of velocity, Vavg,y = _ "yi # y, to update the y component of position? Check all that apply. 2 The ball's velocity changes at a constant rate because the net force on the ball is constant. This formula for average velocity is always valid. The ball's speed is small compared to the speed of light.Z PUB A 'x Z DUE X 2 DUB K A PUB X AJUD A MUD X-Select- it decreases. It increases. It doesn't change.7. [-/13 Points] DETAILS MY NOTES A ball is kicked from a location (9, 0, -8) (on the ground) with initial velocity (-9, 17, -2) m/s. The ball's speed is low enough that air resistance is negligible. (a) What is the velocity of the ball 0.2 seconds after being kicked? (Use the Momentum Principle!) V = m/'s (b) In this situation (constant force), which velocity will give the most accurate value for the location of the ball 0.2 seconds after it is kicked? o the initial velocity of the ball o the arithmetic average of the initial and final velocities O the final velocity of the ball (c) What is the average velocity of the ball over this time interval? Vavg = m/s (d) Use the average velocity to find the location of the ball 0.2 seconds after being kicked. 1 = m Now consider a different time interval: the interval between the initial kick and the moment when the ball reaches its highest point. We want to find how long it takes for the ball to reach this point, and how high the ball goes. (e) What is the y-component of the ball's velocity at the instant when the ball reaches its highest point (the end of this time interval)? Vyf = m/s (f) Fill in the missing numbers in the equation below (update form of the Momentum Principle: mvy = mvy + Fnet, ,At). m = m -mgAt (g) How long does it take for the ball to reach its highest point? At = S (h) Knowing this time, first find the y-component of the average velocity during this time interval, then use it to find the maximum height attained by the ball. Ymax = m Now take a moment to reflect on the reasoning used to solve this problem. You should be able to do a similar problem on your own, without prompting. Note that the only equations needed were the Momentum Principle and the expression for the arithmetic average velocity. Additional Materials WeBook