on a serve, you are able to cross the back line with your foot prior to hitting the ball. true or false. this is for PE

Pls pls pls pls ! describe, in your own words, how you found the epicenter of the earthquake.

Aball with a mass of 275 g is dropped from rest, hits the floor and rebounds upward. if the ball hits the floor with a speed of 2.40 m/s and rebounds with a speed of 1.70 m/s, determine the following. (a) magnitude of the change in the ball's momentum (let up be in the positive direction.)

What does si stand for,when referring to a system of measurement