A rock is projected upward from the surface of the moon, at time t = 0.0 s, with a velocity of 30 m/s The acceleration due to gravity at the surface of the moon is 1.62 m/s2. The height of the rock when it is descending with a velocity of 20 m/s is closest to:

(A) 145 m

(B) 155 m

(C) 135 m

(D) 125 m

(E) 115 m

correct option is B i. e. 155 m

Explanation:

by equation of motion we have

v^2 = u^2 + 2as

where

u is initial velocity = 30 m/s

v is descending velocity = 20 m/s

a is acceleration due to gravity = 1.62 m/s^2

s is height of rock

so we have height at descending is

20^2 = 30^2 - 2*1.62*s

s = 154.32 m

so correct option is B