# Momentum/Collision/Energy Questions

• physicswannab

#### physicswannab

The following three questions are from my physics class regarding collisions:

1. A person attempts to knock down a large wooden bowling pin by throwing a ball at it. The person has two balls of equal size and mass, one made of rubber and the other of putty. The rubber ball bounces back, while the ball of putty sticks to the pin. Which ball is most likely to topple the bowling pin?

I'm thinking that either one since they both had the same amount of momentum/energy before the collisions, but I'm just not sure...

2. Think fast! You've just driven around a curve in a narrow, one-way street at 25 mph when you notice a car identical to yours coming straight toward you at 25 mph. You have only two options: hitting the other car head on or swerving into a massive concrete wall, also head on. In the split second before the impact, you decide to
*
a. hit the other car.
b. hit the wall.
c. hit either one-it makes no difference.

I want to say c because my change in momentum would be the same. again...just not sure.

3. Two pucks collide on a frictionless surface. Puck 1 has twice the inertia of Puck 2. Before the collision, Puck 1 is moving at 20 m/s. Following the collision, the speed of Puck 2 is:

a. less than the initial speed of Puck 1
b. greater than the initial speed of Puck 1
c. equal to the initial speed of Puck 1
d. could be any of the answers above
e. none of the above

Thanks!

The following three questions are from my physics class regarding collisions:

1. A person attempts to knock down a large wooden bowling pin by throwing a ball at it. The person has two balls of equal size and mass, one made of rubber and the other of putty. The rubber ball bounces back, while the ball of putty sticks to the pin. Which ball is most likely to topple the bowling pin?

I'm thinking that either one since they both had the same amount of momentum/energy before the collisions, but I'm just not sure...

True, so you must have to base your answer on the momentum/energy after the collision - i would go with momentum

2. Think fast! You've just driven around a curve in a narrow, one-way street at 25 mph when you notice a car identical to yours coming straight toward you at 25 mph. You have only two options: hitting the other car head on or swerving into a massive concrete wall, also head on. In the split second before the impact, you decide to
*
a. hit the other car.
b. hit the wall.
c. hit either one-it makes no difference.

I want to say c because my change in momentum would be the same. again...just not sure.

Can you be sure the change will be the same? Justify that answer

3. Two pucks collide on a frictionless surface. Puck 1 has twice the inertia of Puck 2. Before the collision, Puck 1 is moving at 20 m/s. Following the collision, the speed of Puck 2 is:

a. less than the initial speed of Puck 1
b. greater than the initial speed of Puck 1
c. equal to the initial speed of Puck 1
d. could be any of the answers above
e. none of the above

OK, try a few examples and see what you get. Twice the inertia means twice the mass. Do these pucks bounce off each other elastically or stick together?
For starters have puck 2 stationary, and the collision head on.
Now try Puck 2 tavelling at the same speed and approaching
Now try puck 2 traveling slower and approaching
Now try puck 2 traveling faster and approaching
Now try puck 2 traveling slower, but in the same direction.
Doe sthe answer meet the same condition every time?
Can you think of an example where the answer would be different?

Thanks!

Some suggestions above.