Question

A stone of mass 4kg is released from tower of height 120 m. Falls freely to the ground. find out the time taken by the stone to reach the ground.

Answer 1

v2 = u2 + 2as
v2 = 2* 10*120
v2 = 2400
v = 48.98 m/s
Now,
v= u + at
48.98 = 10*t
48.98 = 10t
t = 48.98/ 10
t= 4.8 sec.

Answer 2

The time taken by the stone to reach the ground is 4.94 seconds.

Explanation:

It is given that,

Mass of the stone, m = 4 kg

Height of the tower, h = 120 m

We need to find the time taken by the stone to reach the ground. Using second equation of motion to find it as follows :

$h=ut+\dfrac{1}{2}at^2$

a = g and u = 0

$h=\dfrac{1}{2}gt^2$

$t=\sqrt{\dfrac{2h}{g}}$

$t=\sqrt{\dfrac{2\times 120\ m}{9.8\ m/s^2}}$

t = 4.94 seconds

So, the time taken by the stone to reach the ground is 4.94 seconds. Hence, this is the required solution.

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