Part A: Momentum
1. Consider a field of insects, all of which have essentially the same mass. If the total momentum of the
insects is zero, what does this imply about their motion?
2. A rollerskate and a truck are rolling along the road at 2 m/s. Which has the greater momentum?
3. Determine the momentum of a ...
a. 60-kg halfback moving eastward at 9 m/s.
b. 1000-kg car moving northward at 20 m/s.
c. 40-kg freshman moving southward at 2 m/s.
d. 110 kg football player running at 8 m/s forward.
4. A car possesses 20,000 units of momentum. What would be the car's new momentum if…
a. its velocity were doubled.
b. its velocity were tripled.
c. its mass were doubled (by adding more passengers and a greater load)
d. both its velocity were doubled and its mass were doubled.
5. Compare momentum of the player in (3d) with that of a hard-thrown .410 kg football that has a speed of
25 m/s.
6. A cement truck full of cement has a mass of 42,000 kg. It travels north at a speed of 18 m/s.
a. Calculate the truck’s momentum.
b. How fast must a 750 kg Chevy travel to have the same momentum?
Part B: Momentum Conservation
1. Explain why it is difficult for a firefighter to hold a hose that ejects large amounts of high-speed water.
2. A large truck and a Volkswagen have a head-on collision.
a. Which vehicle experiences the greatest force of impact?
b. Which vehicle experiences the greatest impulse?
c. Which vehicle experiences the greatest momentum change?
d. Which vehicle experiences the greatest acceleration?
3. Would you care to fire a rifle that has a bullet ten times as massive as the rifle? Explain.
4. A truck loaded with sand is moving down the highway in a straight path. What happens to the
momentum of the truck if the truck’s velocity is increasing? What happens to the momentum of the
truck if sand leaks at a constant rate through a hole in the truck bed while the truck maintains a constant
velocity?
5. Gymnasts always perform on padded mats. Use the impulse=momentum theorem to discuss how these
mats protect the athletes.
6. The diagram to the right depicts the before- and after-collision speeds of a
car, which undergoes a head-on-collision with a wall. In Case A, the car
bounces off the wall. In Case B, the car "sticks" to the wall.
a. In which case (A or B) is the change in velocity the greatest?
Explain.
b. In which case (A or B) is the change in momentum the greatest?
Explain.
c. In which case (A or B) is the impulse the greatest? Explain.
d. In which case (A or B) is the force which acts upon the car the greatest (assume contact times are
the same in both cases)? Explain.
7. When a car collision occurs, an air bag is inflated, protecting the passenger from serious injury. Explain
how the air bag softens the blow.
8. If you jump from a table onto the floor, are you more likely to be hurt if your legs are relaxed or if your
legs are stiff and your knees are locked? Explain.
9. As a ball falls toward Earth, the momentum of the ball increases. How would you reconcile this
observation with the law of conservation of momentum?
10. If we throw a ball horizontally while standing on roller skates, we roll backward with a momentum that
matches that of the ball. Will we roll backward if we go through the motion of throwing the ball without
letting go of it? Explain.
11. A 15-kg medicine ball is thrown at a velocity of 20 km/hr to a 60-kg person who is at rest on ice.
The person catches the ball and subsequently slides with the ball across the ice. Determine the
velocity of the person and the ball after the collision.
12. A 0.105-kg hockey puck moving at 48 m/s is caught by a 75-kg goalie at rest. With what velocity does
the goalie slide on the ice after catching the puck?
13. A 35.0-g bullet strikes a 5.0-kg stationary wooden block and embeds itself in the block. The block and
bullet move together at 8.6 m/s. What was the original velocity of the bullet? (CAUTION: Be careful of
the units on velocity.)
14. A 3000-kg truck moving rightward with a speed of 10 km/hr collides with a 1000-kg car at rest. The car
moves with a velocity of 15 m/s after the collision. Determine the post-collision velocity of the truck.
15. During a goal-line stand, a 75-kg fullback moving eastward with a speed of 8 m/s collides head-on with
a 100-kg lineman moving westward with a speed of 4 m/s. The two players collide and stick together,
moving at the same velocity after the collision. Determine the post-collision velocity of the two players.
16. Imagine that you are hovering next to a space shuttle in earth orbit and your buddy of equal mass who is
moving at 4 km/hr (with respect to the ship) bumps into you. If she holds onto you, how fast do you
move (with respect to the ship)?
Part C: Impulse
1. The car of a toy train rests on a level track. Will its speed increase more if (a) hit from the rear by a wad
of clay that sticks to the car or (b) hit by a superball of equal mass and velocity that rebounds in the
opposite direction after hitting the car? Explain.
2. In a phun physics demo, two identical balloons (A
and B) are propelled across the room on horizontal
guide wires. The motion diagrams (depicting the
relative position of the balloons at time intervals of
0.05 seconds) for these two balloons are shown
below.
a. Which balloon (A or B) has the greatest acceleration? Explain.
b. Which balloon (A or B) has the greatest final velocity? Explain.
c. Which balloon (A or B) has the greatest momentum change? Explain.
d. Which balloon (A or B) experiences the greatest impulse? Explain.
3. A hockey player applies an average force of 80.0 N to a 0.25 kg hockey puck for a time of 0.10 seconds.
Determine the impulse experienced by the hockey puck.
4. If a 5-kg object experiences a 10-N force for a duration of 0.1-second, then what is the momentum
change of the object?
5. What is the average force exerted on a .140 kg baseball by a bat, given that the ball’s initial velocity is
45 m/s and that its final velocity, after a 1.3 X 10-3 s impact, is 65 m/s in exactly the opposite direction?
(1.18 X 104 N)
6. Calculate the final speed of a 110 kg football player initially running at 8 m/s who collides head on with
a padded goalpost and experiences a backward force of 1.76 X 104 N for 5.50 X 10-2 s. (-.800 m/s)
Part D: Review All
1.
A 2-kg object initially at rest is acted upon by a single force in
direction in a manner described by the graph shown. The
momentum acquired by the object is
the x
2. A 0.040-kg bullet traveling at 400 m/s hits and embeds itself in a 0.20-kg wooden block resting on a horizontal frictionless surface.
The speed of the bullet-block system immediately after the collision is closest to
3. Two boxes on a frictionless air track are forced together with a compressed spring between them. After the boxes, initially at rest,
are released, Box B (mB = 2kg) moves right at a speed of 3.0 m/s, as shown in the figure. When the boxes are released, they move
apart. What is the momentum before the collision? What is the speed of Box A after release?
A
V
3 m/s
4 kg
2 kg
4. A 2-kg object is moving at 3 m/s toward the right. A 4-N force is suddenly applied pointing opposite the direction of motion
(toward the left). The force acts for a time interval of 4 s, and then is removed. What is the final velocity of the object?
5. A hockey player applies an average force of 80.0 N to a 0.25 kg hockey puck for a time of 0.10 seconds. Determine the impulse
experienced by the hockey puck.
6. A car possesses 20,000 units of momentum. What would be the car's new momentum if its velocity were doubled?
Use the following information to answer questions #7 – 10.
Unfortunately, Anna Litical was in a car accident. Her Volkswagon Beetle was hit by an 18-wheeler (a giant Mac truck). She survived
because she wore her seatbelt and had driver’s side airbags, but her car was crumpled up. Use the following choices to answer each
question.
a. The truck’s is bigger than the Beetle’s.
b. The truck’s is smaller than the Beetle’s.
c. Neither, they are equal but opposite.
d. Can’t tell without more information.
7.
Which vehicle delivers a bigger force?
8. Which vehicle has a bigger acceleration during the collision?
9. Which vehicle received the bigger impulse?
10. Which vehicle had the bigger change in momentum?
11. Which has the bigger initial speed?
Use the information below to answer questions #12 – 14.
A male figure skater and a female figure skater are at rest together in the middle of the rink. The male skater, who has a much bigger
mass than the female, releases the woman by pushing her away from him forcefully.
12. Which skater has a bigger momentum after release?
a. After release, the magnitude of the momentum of the man equals that of the woman.
b. After release, the magnitude of the momentum of the man is greater than that of the woman.
c. After release, the magnitude of the momentum of man is less than that of the woman after release.
d. Not enough information to make conclusions about the relative magnitudes of the momenta of the skaters.
13. How does the total momentum of the skaters before release compare to the total momentum of the skaters after release?
(a) The total momentum of the skaters after release is the same as before release.
(b) The total momentum of the skaters after release is greater than before release.
(c) The total momentum of the skaters after release is less than before release.
(d) Not enough information to make conclusions about the total momentum of the skaters.
14. After release, how does the speed of male skater compare to the speed of the female skater?
a. The speed of male skater is the same as that of the female skater at all times after release.
b. The speed of male skater is greater than that of the female skater at all times after release.
c. The speed of male skater is less than that of the female skater at all times after release.
d. Not enough information to make conclusions about the relative speed of the skaters.
15. A 2500-kg SUV moving eastward with a speed of 28 m/s collides head-on with a 1320-kg sedan moving westward with a
speed of 24 m/s.
a) If the truck continues in its original direction at 10 m/s after the collision, what is the final velocity of the car?
b) Is this collision elastic or inelastic? Prove it!
c) Draw a qualitative Force-time graph for the SUV.
d) If the SUV had crashed into a softer object, let’s say a padded wall, how would the Force-time graph change? Assume
that the initial speed remained exactly the same.
e) How does the impulse received by the SUV compare to the impulse received by the sedan?
f) Which has the bigger change in velocity?
16. A football player kicks a 0.75 kg football with a force of 1200 N. His foot is in contact with the ball for 0.0016 seconds.
a) At what velocity did the ball leave the ground?
b) What horizontal range did the ball go, if he kicked the ball at an angle of 60 degrees above the horizontal? (5 POINTS)
HINT: this is a 2-step projectile problem!
c) For what distance did the player’s foot remain in contact with the ball?
17. A railroad diesel engine has a mass of 10,000 kg, which is 4 times the mass of a flatcar. The diesel coasts at 5 km/hr into a flatcar
that is initially at rest.
a. How fast do the two coast if they couple together?
b. How far do they coast before stopping if friction is 1000-N?