Question

Question 40:
A stone is dropped from a height of 20 m.
(i) How long will it take to reach the ground ?
(ii) What will be its speed when it hits the ground ? (g =10 m/s2)

Lakhmir Singh Physics Class 9

Answer 1

Answer:

Given

u = 0 m/s

g = 10 m/s^2

h = 20 m

Now using

s = ut + 1/2 at^2

that is

h = ut + 1/2 gt^2

Now substitute the value

20 = 0*t + 1/2 * 10 (t)^2

20 = 5(t)^2

(t)^2 = 4

t = 2s

Now again using

V = u + at

V = 0 + 10 * 2

V =20 m/s

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