Comparing Speed and Kinetic Energy in a Railroad Car Collision

[mitchmcsscm94]

Test corrections!

Homework Statement

1.) a railroad car of mass m is moving with speed v when it collides with and connects to a second railroad car of mass 3m, initially at rest. how do the speed and kinetic energy of the connected cars compare to those of the single car of mass m before the collision.
speed/Kinetic Energy

a.)less,less​

b.)less,the same​

c.) the same, less​

d.) greater, the same​

2.) a ball of mass m and momentum p has kinetic energy equal to which of the following?

a.) 1 p²/2 m​

b.) p²/m​

c.)2 (p²/m)​

d.)1m/2p²​

3.) a new planet is discovered that is twice the Earth's mass and twice the Earths radius. On the surface of this new planet, a person who weights 500N on Earth would experience a gravitational force of

a.)125N​

b.)250N​

c.)500N​

d.)1000N​

Homework Equations

The Attempt at a Solution

1 is not b
2 is not b
3 is not c

 

[SammyS]

What have you tried?

Where are you stuck?

Can you give any reasons as to why the listed answers are wrong?

A hint for #2: What is the formula for p? Pk\lug that formula in for p in the four choices. See if any of them result in the formula for kinetic energy.