Question

A rock is thrown vertically upwards with initial positive velocity of 30 m/s. What will be the maximum height that the rock will reach and when will it reach it

Answer 1

Vi = 30 m /sec

Vf = 0 ( at max. height)

g = - 9.8 m/ sq. sec. ( -ve sign shows that the motion of the body is in opposite direction to that of gravity)

Height it gains=h = ?

Using 3rd equation of kinematics,

2ah=Vf ˄2 – Vi˄2

implies that

h = Vf ˄2 – Vi˄2 / 2a

h = 0˄2 - (30)˄2 / 2(-9.8) = - 900/ -19.6

h = 45.91 m

So the maximum height the body can gain is approximately equal to 46 m.

Note: in simple approximation if we take g = 10 m/ sq.sec then the max. height the body can attain will be 45 m.