Please help me... :(

Question

There is a moving bowling ball on the track. A student says, "After the ball is thrown horizontally on the wooden track with horizontal velocity v and zero angular velocity, the translational kinetic energy of the ball remains unchanged before it hits the pins since the track is frictionless." Is this statement true or false, and why?

Another student asserts that the momentum of the bowling ball and the pins is conserved during the collision of the ball and the pins. What assumptions and conditions required for making such a comment?

If a bowling ball of greater mass is used instead, what will be the difference in the effect on the collision between the bowling ball and the pins?

I am really desperate for help... Thanks in advance.

Answer 1

But bowling balls roll.
If there were truly no friction between track and ball, the hypothesis that the translational kinetic energy remains constant and the angular velocity remains zero could be true, but we all know the ball starts rolling.
The rolling means first that a force is exerted between track and ball that is in the direction to the translational motion while accelerating the rotational motion. Thereby translational kinetic energy decreases and rotational increases. As the ball proceeds down the track it achieves a "no slip" condition where the angular velocity times the radius equals the translational speed and there is no longer relative motion between track and ball at the contact point. It is then rolling and not sliding.

Answer 2

In "Paul's Case," why does Paul go to work early? A. He wanted to wrestle with the other boys.
B. He didn't want to get caught skipping school.
C. He liked looking at the pictures in the art gallery.
D. He didn't want to lose his job.