Question

A stone is dropped from a height of 10 m on an unknown planet having g = 20 m/s2. Calculate the speed of the stone when it hits the surface of the planet. Also calculate the time it takes to fall through this height.

CBSE Class IX Science SA 2 (3 Marks)

Answer 1

u = 0

h = 10m

g = 20m/s2

v = root: u2 + 2gh

0+2×20×10


=20m/s

v = u+gt

t= v/g

20/20

= 1s
HOPE IT HELPS YOU!!!

Answer 2

Given: A stone is dropped from a height of 10 m on an unknown planet having g = 20 m/s2.

To find: We have to find the final speed of the stone and the time required to fall.

Solution:

We know that,

${u}^{2} + {v}^{2} = 2gh$

Where u is the initial speed of the stone and v is the final velocity of the stone.

g is the gravitational force 20m/s^2.

h is the height 10m.

u is 0.

${v}^{2} = 2 \times 20 \times 10 \\ v = \sqrt{400} \\ v = 20$

The speed of the stone when it hits the surface of the planet is 20m/s.

Again we know that

v=u+gt

20=0+20×t

t=1

The time it takes to fall through this height is 1 second.