Question

If a ball is thrown upwards with a velocity of 20m/s find the time for which the ball will remain in the air?

Answer 1

Using Newton's law of motion,
v = u + at

(Where v is the final velocity, u is the  initial velocity, a is the acceleration and t is the time taken)

Putting in values (Final velocity is taken to be 0, and a = 10m/s (gravity) with upwards direction to be positive),
we get

0 = 20 - 10 * t
t = 2 sec.

This is the upward travel time of the ball. Downwards travel time is equal to this. So the ball will remain in the air for a total of 4 seconds.