When a 1.0 kg object rest on your foot for 0.10 s, the impulse exerted is -0.98 Ns. It's t/f. The formula for impulse is (Please correct me if I'm wrong) force=(mass*velocity)/time So wouldn't it be force=(1.0*9.8)/0.10 = 9.8/0.10 = 98. Right ? How do you know if it's supposed to be negative ? Or is it negative because it is falling ? I don't know.. Thanks for helping though !

Question

noelgreco · Answer

$$Impulse = F \Delta t = \Delta p$$
Imagine kicking a football.  The ball does not really "rest" on your foot, but is in contact with it for a certain time.

The impulse of the ball on your foot is negative; the impulse of your foot on the ball is positive.

"So wouldn't it be force=(1.0*9.8)/0.10 = 9.8/0.10 = 98."

No, it would be 1.0 * 9.8 * 0.10 = .98.  Add the negative depending on the direction of the impulse.

anonymous · Answer

Ohh. Okay. I understand. Thanks, the football made it easy to see what your saying. Thanks !