15.An object projected vertically upwards with an initial velocity 40m/s from the ground(g=10m/s2).The time taken by the object to reach the maximum height

solution:

The object projected vertically upwards an initial velocity(u)=40m/s

if the object to reach the maximum height, the final velocity will be zero.

from kinematic equations ,we have the formula,

(v)²-(u)²=2as

here , v=0,u=40m/s, a=-g=10m/s²

0-40*40=2(-10)S

-1600=-20S

S=80m

here, distance is nothing but maximum height .