Question

A stone is thrown vertically upwards with a speed of 20m/s. The time(in seconds) taken by it to come back to its point of projection is (take g=10m/s2 (10 metre per second square))

Answer 1

initial velocity is 20mper sec
acceleration is -10 mpersec square
final velocity is 0
time taken to reach top pt is

v-udivided by t=a
0-20/t=-10
-20=-10 t
t=2sec

total time taken =time taken in going up +time taken in coming down
2×2 =4sec
time taken in going up is always equal to time taken in coming down