Question

A stone is dropped from a height of 30 m.after 2 seconds it's height from the earth will be:
Options:
A-10 m
B- 15m
C-20m
D- 5m

Answer 1

it's height from the earth after 2 sec will be 10 meters.

Explanation:

Given ,

initial speed, u = 0

time = 2 sec

acceleration, a = acceleration due to gravity = 10 m/s²

Hence according to the law of motion equation the distance covered by the stone in 2 sec will be,

S = ut + at²/2

= 0 + 10 x 4/2

= 20 meters

Initial height, = 30 m

Final height = initial height - distance covered = 30 - 20 = 10 m

Hence it's height from the earth after 2 sec will be 10 meters.

Answer 2

A stone is dropped from a height of 30 m.after 2 seconds it's height from the earth will be:  

Options:

A-10 m

B- 15m

C-20m

D- 5m

Stone is dropped so initial speed = 0 m/s

S = ut + (1/2)at²

S = Distance Covered

u = initial speed = 0 m/s  (dropped)

t = 2 sec

a = 10 m/s²  acceleration due to gravity

S = 0  + (1/2) 10 * 2²

S = 20 m

Earlier Stone was at height of 30 m

20 m distance covered in 2 sec

Height after 2 sec = 30 m - 20m = 10 m

Option A - 10 m