Ryan is demonstrating inelastic collisions by standing on a stationary skate board, and
catching a bowling ball thrown at him as shown here:
a) On his first attempt, he tenses up and keeps his arms "stiff" while catching the ball. After
experiencing a great deal of pain in his hands, Ryan relaxes and decides to repeat the
experiment using "soft hands", while allowing the ball to gradually come into his body. In the
chart below, analyze the listed physics principle. Place a check in the box of the trial you
believe would have a greater value. If you believe they would be the same, place a check mark
in each box. Justify your answers with an explanation for each and you can assume that in
each case, the ball is thrown with the same initial velocity, and there is no friction between the
skate board and the ground.
Physics Principle
Time to stop ball
Force exerted by hands
on ball
"Stiff Hands Trial
"Soft' Hands Trial
Change in speed of the
ball while being caught
Change in speed of Mr.
Graves while catching
the ball
b) If Ryan weighs 10 times more as the ball, what will be the ratio of the initial speed of the ball
before being caught to the final speed of both the ball and Ryan after he demonstrates his
athleticism by catching the ball successfully?
c) Explain why the kinetic energy of the ball before Ran catches it must be greater than the
combined kinetic energy of the ball and Ryan after the catch.
d) In a third attempt, Ryan decides to deflect the ball back towards the direction it originally
came from. Woe his change in speed be greater, less than, or the same as to when he caught
the ball? Explain.
