* Note: Circled Problems Are to Be Completed by Honors Students Only

Impulse / Momentum Review (HON/ACCEL) Lyzinski, Physics

* Note: circled problems are to be completed by honors students only

1. A 2500 kg car traveling to the North is slowed down uniformly from an initial velocity of 20 m/s by a 6,250 N braking force acting opposite the car’s motion.

a) What is the car’s velocity after 2.5 seconds? b) How far does the car move during 2.5 seconds? c) How long does it take for the car to come to a complete stop?

2. A 47.4 kg student runs down the sidewalk and jumps with a horizontal speed of 4.20 m/s onto a stationary skateboard. The student and skateboard move down the sidewalk with a speed of 3.95 m/s. Find the following:

a) the mass of the skateboard. b) how fast the student would have to jump to have a final speed of 5 m/s. c) the energy loss that occurred during part “b” above.

3. A boy stands at one end of a long floating raft that is stationary relative to the shore. He then walks in a straight line to the opposite end of the 8 foot long raft , away from the shore.

a) Does the raft move? Explain. b) What is the total momentum of the boy and the raft before the boy walks across the raft? c) What is the total momentum of the boy and the raft after the boy walks across the raft? d) If the raft has a mass of 200 kg, and the boy has a mass of 70 kg, find the speed that the raft acquires if the boy walks with a constant speed of 5 m/s. e) How much closer to the shore is the boat now, compared to when he started walking.

4. High-speed stroboscopic photographs show the head of a 215 gram golf club traveling at 55 m/s just before it strikes a 46g golf ball at rest on a tee. After the collision, the club travels (in the same direction) at 42 m/s. find the speed of the golf ball just after impact. Was the collision Elastic or Inelastic. Fully explain your rationale.

5. A billiard ball of mass 200g rolls toward the right-hand cushion of a billiard table at 2 m/s and rebounds straight back at 2 m/s.

a) What is the change in momentum as a result of hitting the cushion? b) What impulse is given to the ball by the cushion?

6. A hockey puck of mass 0.20 kg is sliding along a smooth, flat section of ice at 18 m/s when it encounters some snow. After 2.5 seconds of sliding through the snow, it returns to smooth ice, continuing at a speed of 10 m/s.

a) What is the change of momentum of the puck? b) What impulse does the snow exert on the puck? c) What average frictional force does the snow exert on the puck?

7. A 3 meter long pendulum with a 4 kg bob on its end is loaded to a 50o angle and then released. At the bottom of its swing it collides head on and elastically with a 500 gram object. Find the speed of the 500 gram object after the collision, as well as the angle that the pendulum bob will rise back to after the collision.

8. A force of 5 Newtons directed South is applied for 10 seconds to a 4 kg object that is moving at 4 m/s Northeast. Find the final velocity of the object after these 10 seconds. 9. The graph at the right shows the magnitude of the retarding force exerted to an object to slow it down during a collision. If the object has a mass of 50 kg and is traveling at 10 m/s before the collision, find:

a) the total impulse delivered to the object. b) the final speed of the object. c) the speed of the object after 12 seconds. d) the object’s momentum after 14 seconds.

10. A 10,000 kg truck traveling at 30 m/s [N 40o E] collides with a 1,500 kg car traveling at 45 m/s [S 20 o W]. If the cars stick together, find their velocity (magnitude and direction) after the collision.

11. A 10 kg bomb explodes into 4 pieces. The first 2 kg piece travels South at 50 m/s. The second 3 kg piece travels West at 35 m/s. The third 1 kg piece travels northeast at 40 m/s. Find the velocity (magnitude and direction) of the final piece.

12. A 1000 kg car is moving at a speed of 40 m/s to the right when it rear-ends a 1500 kg car, which was moving at a speed of 30 m/s to the right. Their bumpers compress like springs, but permanent deformation does NOT take place, and thus energy is conserved. Find the maximum Potential Energy stored in the bumper at the time of the crash.

13. Two motion carts, each of mass 5 kg move towards each other, both at a speed of 4 m/s. An 8000 N/m Ideal Spring sits between them, attached to one of the cars. If the spring’s un-smushed length is 50 cm, find the minimum separation between the cars during the collision.

14. A 500,000 kg space-ship that is 40 meters long is resting in deep space. It can be assume that all the mass on this spaceship is evenly distributed. Six 80 kg astronauts are sitting 2 meters from the end of the ship in a conference room. The meeting ends and all six astronauts walk out. Two stop at the coffee machine, which is located at the center of the ship, while the other 4 move to another conference room, where they all sit 3 meters from the opposite end of the ship that they were just sitting on.

a) Find the distance that the ship has moved once all “resettling” of astronauts has been completed. b) Each astronaut reaches the midpoint of their journey at the same time, and each astronaut is walking at a brisk 5 m/s at this moment in time. Find the speed of the ship at this moment.

15. An elastic collision takes place between two objects, one of mass 60 kg moving at a velocity of 40 mi/h South and the other of mass 30 kg moving at a velocity of 50 mi/h North. Find the velocities of the objects after the collision.

16. A 20 kg mass is moving at 5 m/s (along a frictionless surface) when it strikes a 50 kg pendulum bob (which is attached to a 10 m long string). WOW, THAT’S ONE BIG PENDULUM!!!! The 20 kg mass bounces backwards at a quarter of its original speed. Find the angle of the pendulum’s swing.

17. A 3 kg mass is moving at 7 m/s (along a frictionless surface) when it strikes a 4 kg mass which is sitting at rest at the bottom of a 40o hill. The blocks stick together, ann begin to move up the hill. Find the height that they rise to (before stopping) as well as the distance uphill that they moved.

18. A 50 gram block is sitting against a spring, which is initially unstretched. A 70 gram block moving at 3 m/s runs into the 50 gram block. After the collision, the 70 gram block stops dead in its tracks, and the 50 gram block starts to compress the spring. If the spring smushes 20 cm, find the spring constant of the spring. Explain why this problem seems “IMPOSSIBLE” from an energy standpoint.