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Physics 1120 In-Class Problems: Momentum and Impulse

  1. The diagrams below are graphs of Force in kiloNewtons versus time in milliseconds for the motion of a 5-kg block moving to the right at 4.0 m/s.
    (a) What is the magnitude and direction of the impulse acting on the block in each case?
    (b) What is the magnitude and direction of the average force acting on the block in each case?
    (c) What is the magnitude and direction of the final velocity of the block in each case?

  2. The diagrams below are the velocity versus time graphs for the collision of motion of a 4-kg block with a wall. The collision lasts for 20 milliseconds in each case.
    (a) What is the magnitude and direction of the impulse acting on the block in each case?
    (b) What is the magnitude and direction of the average force acting on the block in each case?

  3. You've been rowdy and obnoxious in a bar and are now in the process of being thrown out by the scruff of the neck by the bouncer. The bouncer has hold of you for 5.0 s and you are take from a seated position to a final speed of 2.75 m/s. If your mass is 70.0 kg, what was your final momentum? What impulse and average force did the bouncer exert on your person? Assume all motion is in a straight line.

  4. A ball of mass 0.500 kg with speed 15.0 m/s collides with a wall and bounces back with a speed of 10.5 m/s. If the motion is in a straight line, calculate the initial and final momenta and impulse. If the ball exerted an average force of 1000 N on the wall, how long did the collision last?

  5. A ball of mass 0.25 kg glances of a wall as shown in the diagram. The ball approaches at 15 m/s at θ = 30° and leaves at 12 m/s at φ = 20°. The collision lasts for 15 milliseconds.
    (a) What are the components of the impulse experienced by the ball?
    (b) What are the components of the average force acting on the ball?

  6. Explain why a person wearing a seatbelt in a car accident is less likely to be seriously hurt than the person who isn't wearing a seatbelt.

  7. A lion of mass 120 kg leaps at a hunter with a horizontal velocity of 12m/s. The hunter has an automatic rifle firing bullets of mass 15 g with a muzzle speed of 630m/s and he attempts to stop the lion in midair. How many bullets would the hunter have to fire into the lion to stop its horizontal motion? Assume the bullets stick inside the lion.

  8. On a frictionless surface, a 6.0-kg rock approaches from the left at 3.5 m/s. It collides elastically with a 9.0-kg rock which is approaching from the right at 1.7 m/s.
    (a) Without changing coordinate systems, find the final velocities of the rocks.
    (b) Use a coordinate system in which the 9.0-kg rock is not moving to find the final velocities of the rocks.
    (c) Use a coordinate system in which the 3.5-kg rock is not moving to find the final velocities of the rocks.

  9. If the collision in question #2 had been perfectly inelastic, what would have been the final velocity of the rocks? How much kinetic energy would have been lost in the collision?

  10. If the collision in question #2 had a coefficient of restitution e = 0.600, what would have been the final velocity of the rocks? How much kinetic energy would have been lost in the collision?

  11. A 50.0-kg skater is traveling due east at 3.00 m/s. A 70.0-kg skater is moving due south at 7.00 m/s. They collide and hold on to one another after the collision. Determine the magnitude and direction of their velocity after the collision. Ignore the effects of friction.

  12. A curling rock is traveling down the ice when it mysteriously explodes into three parts. After the explosion, one piece having 27.0% of the total mass moves at a speed of V1f = 14.2 m/s at an angle of 42.0° to the positive y axis. A second with 52.0% of the total mass move at a speed of V2f = 18.9 m/s at an angle of 17.8° to the positive x axis. The third piece moves with speed V3f = 35.9 m/s at 39.0° to the negative y axis. What was the speed of the stone before the explosion?

  13. In a pool game, balls of the same mass undergo elastic collisions. Suppose the white ball collides with a stationary 8-ball off-centre. After the collision, both balls travel at an angle to the original velocity of the white ball as shown in the diagram. If the initial speed of the white ball is v and θ = 30.0°, determine φ and the speeds of the balls.

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