1)After falling 19 m , a 0.057-kg tennis ball has a speed of 15 m/s (the ball\'s

Question

1)After falling 19 m , a 0.057-kg tennis ball has a speed of 15 m/s (the ball's initial speed is zero).

A)Determine the average resistive force of the air in opposing the ball's motion.

B)Does the solution of problem depend on the choice of system of the ball?

2)A Frisbee gets stuck in a tree. You want to get it out by throwing a 1.0-kg rock straight up at the Frisbee.

If the rock's speed as it reaches the Frisbee is 4.0 m/s, what was its speed as it left your hand 2.8 m below the Frisbee?

Explanation / Answer

1) A. using v^2 - u^2 = 2ad

15^2 - 0 = 2 x a x 19

a = 5.92 m/s^2

in vertical on ball, mg - F = ma

F = mg - ma =0.057(981 - 5.92) =0.22 N

2) using v^2 - u^2 = 2ad

4^2 - u^2 = 2 x -9.81 x 2.8

u =8.42 m/s

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