Explore BrainMass

# relative velocity and work done by the train

Not what you're looking for? Search our solutions OR ask your own Custom question.

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

A train moves along the tracks at a constant speed u. A woman on the train throws a ball of mass m straight ahead with a speed v with respect to herself.
a) What is the kinetic energy gain of the ball as measured by a person on the train?
b) By a person standing by the railroad track?
c) How much work is done by the woman throwing the ball and the train?
d) how much work is done by the train?

https://brainmass.com/physics/velocity/relative-velocity-work-done-train-112860

## SOLUTION This solution is FREE courtesy of BrainMass!

A train moves along the tracks at a constant speed u. A woman on the train throws a ball of mass m straight ahead with a speed v with respect to herself. What is the kinetic energy gain of the ball as measured by a person on the train? By a person standing by the railroad track? How much work is done by the woman throwing the ball and the train?

(a) The initial velocity of the ball relative to the train is 0. The velocity of the ball relative to the train is v after it was thrown out.
So the gain of the kinetic energy of the ball is

(b) The initial velocity of the ball relative to the ground u.
After the ball is thrown out, assume the velocity of the ball is x relative to ground.
Then
So the kinetic energy change of the ball is

(c) According to the work-energy theorem, the work done by the woman is equal to the change of the kinetic energy of the ball.

(d) However, we know the total kinetic energy gain of the ball is relative the ground. So the total work done onto the ball is . The extra work muv is done by the train.
So the work done by the train is muv.

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!