http://www.smartphysics.com/images/content/mechanics/ch13/ballhitswall2.png
The racquet ball with a mass of 0.238 kg is moving straight toward the wall at a velocity of vi = 12.8 m/s. The ball makes an inelastic collision with the solid wall and leaves the wall in the opposite direction at vf = -8.1 m/s. The ball exerts the same average force on the ball is 66.108N.

How can I get the change in kinetic energy of the racquet ball?



http://www.smartphysics.com/images/content/mechanics/ch13/explosion3.png
An object with total mass mtotal = 16 kg is sitting at rest when it explodes into three pieces. One piece with mass m1 = 5 kg moves up and to the left at an angle of θ1 = 25° above the –x axis with a speed of v1 = 26.7 m/s. A second piece with mass m2 = 5.2 kg moves down and to the right an angle of θ2 = 30° to the right of the -y axis at a speed of v2 = 21.6 m/s. m3=5.8 kg, and v3 = 13.212 m/s.

What is the increase in kinetic energy of the pieces during the explosion.
I am confused because there is both x and y component, so how can I deal with it?

1. Is that this difficult?

Change in KE = Final KE - Initial KE

Or did you mean momentum?

Or a little harder, but not impossible, the time with which the ball was in contact with the wall?

2. Yes, break all of them into two components, an x and a y component.

The total momentum along the x axis should be 0, and the y coordinate along the y axis should be zero.

I got the first question, but for the second question, I add all the kinetic energy of each piece has and divide by 3, am I right? And I will get 1167.165J?

Ok, I admit that I didn't read the question but only looked at the picture, and it's a lot easier than I previously thought. (I thought that the velocity and mass of 1 and 2 were given and you were required to find the change in kinetic energy of the last particle.)

It uses the same principle as in the first question.

Change in KE = Final KE - Initial KE

Do that for each of the parts formed by the explosion.

For the increase in KE, you just need to calculate the KE for each piece and add them together.
So, increase in KE = 1/2 m1 * v1^2 + 1/2 m2 * v2^2 + 1/2 m3 * v3^2 =...
I just finished this same question. Gudluck!