Momentum and Impulse

Question 1

What are the units for momentum?

Answer 1

kg m/s

Question 2

What are the two ways to solve for impulse?

Answer 2

I = Ft

I = pf - pi

Question 3

What is the impulse exerted on a person who experiences an 85 N net force over 0.7 seconds?

Answer 3

59.5 kg m/s

Question 4

Explain an Inelastic collision scenario and give an example. (in the context of momentum conservation)

Answer 4

In the event of an inelastic collision, two objects collide and stick together. An example of this is two stress balls being rolled toward each other and sticking together, becoming one object.

Question 5

True or False: A larger object always has greater momentum.

Correct and explain if false, explain if true.

Answer 5

False, the momentum of an object depends on velocity as well as mass.

Question 6

True or False: The change in momentum of an object is always equal to the impulse exerted on the object.

Answer 6

True, impulse = Δp

Question 7

If the momentum of an object stays the same, but the mass has tripled, what must have happened to the velocity?

Answer 7

The velocity must have been divided by three.

Question 8

Explain a PERFECTLY elastic collision scenario and give an example.

Answer 8

Any time two or more objects collide and DO NOT stick together. (they don’t need to bounce)
An example of this is driving two Hot Wheels cars into each other, they will collide and go in the opposite direction from how they came. (KE is conserved)

Question 9

How is momentum similar to and different from kinetic energy?

Answer 9

Similar: same variables, deal with motion.
different: momentum is linear and a vector, kinetic energy is scalar and not always conserved in collisions.

Question 10

Which impulse is higher? Why?

A. A school bus, going 30 mph, comes to a stop by running into the side of a building.

B. A school bus, going 30 mph, comes to a stop by slowly pressing on the brakes as it approaches a stop sign.

Answer 10

Both situations have the same momentum because they have the same initial and final momentum.

Question 11

The total momentum of Steven on his bike is 770 kgm/s. What is his mass, if he is riding at 10 m/s?

Answer 11

His mass is 77kg.

Question 12

The recoil momentum of a tank initially at rest is (smaller than/greater than/the same as) the momentum of the projectile that it shoots. Choose one and explain your answer.

Answer 12

The same, the tank has a smaller velocity but a higher mass, the projectile has a smaller mass but a higher velocity. This is because the tank/projectile system starts with a momentum of zero, so according to the Law of Conservation of Momentum, it should end up with a total momentum of 0. This means the tank has some negative momentum and the projectile has a positive momentum, and these must be the same size to add up to zero.

Question 13

If the mass of a wagon is quadrupled by loading more boxes into it, but the momentum of the moving wagon only doubles, what must have happened to the velocity?

Answer 13

The velocity was cut in half.

Question 14

You have a ball of clay and a bouncy ball, both with the same mass. The ball of clay sticks to the door, and the bouncy ball bounces back off the door. If they are both thrown at the same speed, which object, if either, has the greater impulse? Explain

Answer 14

The bouncy ball! Momentum changes more when the object changes direction compared to when it just comes to a stop.

Question 15

A bullet train with a mass of 48,000 kg slows down from 130 m/s to 50 m/s. What is the impulse exerted on the train by the brakes?

Answer 15

-3,480,000

Question 16

A 400 kg paddle boat moves with a velocity of 6.25 m/s collides head-on with a 200 kg raft that started out moving at -2 m/s to the left. If the boat and the raft stick together what is there final velocity?

Answer 16

3.5 m/s

Question 17

A piece of clay at rest is exploded into FOUR pieces. The first piece of clay has a momentum of -10 kg m/s to the left. The second piece has a momentum of 2 kg m/s to the right. The third piece goes to the right with a momentum of 11 kgm/s. What is the momentum of the fourth piece, and in what direction does it move?

Answer 17

-3 kg m/s

Question 18

If two identical eggs are thrown at the same velocity, one at a wall and one at a curtain, what is the difference in the collision that occurs? Use the words impulse, force, and time properly in your explanation.

Answer 18

The impulse on both eggs is the same, but the force on the “wall” egg is much greater because the time of impact is much less, because the wall does not have as much “give” as the curtain.

Question 19

Give an example of a safety feature or technique that can be explained using impulse and explain how it works, using the terms impulse, force, and time.

Answer 19

Kneepads, when one is riding a skateboard or bike are a safety feature as the cushion effect of the kneepad increases the time of the impact.

Question 20

Two kickballs, red and green, roll into each other and bounce off. The red ball, mass of 1.5 kg, is originally moving at 3 m/s to the right, and it hits the green ball which has a mass of .8 kg was originally moving at -5 m/s to the left. After the bounce, the green ball is moving at 4.38 m/s. How fast was the red kickball going after the bounce.

Answer 20

-2 m/s