Book Online Demo

Check Your IQ

Try Test

Courses

A boy standing on a cliff of $480 m$ height, drops a stone. One second later, he throws a second stone after the first. They both hit the ground at the same time. With what speed does he throw the second stone? (Take $= 10 m / s^{2}$ )

see full answer

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!

An Intiative by Sri Chaitanya

5 m / s

10.5 m / s

14.7 m / s

19.6 m / s

answer is B.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

He throw the second stone with the speed of

10.5 m / s

.
Given data and assumptions:
Dropping height,

h = 480 m

Initial velocity of first stone,

u_{1} = 0

(as it is dropped freely.)
Initial velocity of 2nd stone,

= u_{2}

Using 2nd equation of motion for the first stone

h = u_{1} t + \frac{1}{2} g t^{2}

480 = 0 \times t + \frac{1}{2} \times 10 \times t^{2}

t^{2} = \frac{480}{5}

t^{2} = 96

t = 9.8 s

The time taken by the second stone will be

1

second less than the first stone.

t = 8.8 s

Using

2

nd equation of motion for the

2

nd stone

h = u_{2} t + \frac{1}{2} g t^{2}

480 = u_{2} \times (8.8) + \frac{1}{2} \times (10) \times (8.8)^{2}

\Rightarrow

u = 10.5 m / s

Watch 3-min video & get full concept clarity