# Homework Help: Force experienced by a tennis ball

1. Apr 30, 2012

### jmgXD6

A .065-kg tennis ball moving to the right with a speed of 15 m/s is stuck by a tennis racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in contact with the racket for 0.020s, what is the magnitude of the average force experienced by the ball?

F=mv/t I think that's the equation to use.

So if I plug in 0.065 for mass 15 m/s for velocity and .020s for time I would get 48.75 N but that's not an answer choice.

Last edited: Apr 30, 2012
2. May 1, 2012

### ehild

The change of the momentum is equal to the impulse: Δ(mv)=FΔt.

The velocity of the ball turns to opposite. How much does its momentum change if the velocity changes from 15 m/s to -15 m/s?

ehild

3. May 1, 2012

### jmgXD6

It goes from .975 kgm/s to -.975 kgm/s so it changes by 1.95 kgm/s.

4. May 1, 2012

### Staff: Mentor

So does that lead to a match with one of the options offered, now?

5. May 1, 2012

### jmgXD6

So then if thats the case then 1.95 kgm/s=Ft and t equals .020 I would get 97.5 for force but that isn't an answer choice. What am I doing wrong?

6. May 1, 2012

### ehild

97.5 N should be correct.

ehild

7. May 1, 2012

### jmgXD6

I feel dumb now, our teacher likes to round and one of the answer choices is 98. Thanks guys.

8. May 1, 2012

### Office_Shredder

Staff Emeritus
That's not just rounding, that's the teacher correctly using significant figures