Question

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)​

Answer 1

Answer:

Height, s=20m

Initial velocity, u=0

Acceleration due to gravity, g=10 m/s

2

Final velocity, v=?

Time taken, t=?

(i) Using relation,

s=u t+

2

1

gt

2

20=0×t+

2

1

×10×t

2

20=0+5t

2

t

2

=

5

20

=4

t=

4

=2 s

(ii)For a freely falling body:

v

2

=u

2

+2gh

=(0)

2

+2×(10)×(20)

So, v

2

=400

v=

400

=20 m/s

The speed of stone when it hits the ground will be 20m/s.

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Answer 2

Answer:

Height, s=20m

Initial velocity, u=0

Acceleration due to gravity, g=10 m/s

2

Final velocity, v=?

Time taken, t=?

(i) Using relation,

s=u t+

2

1

gt

2

20=0×t+

2

1

×10×t

2

20=0+5t

2

t

2

=

5

20

=4

t=

4

=2 s

(ii)For a freely falling body:

v

2

=u

2

+2gh

=(0)

2

+2×(10)×(20)

So, v

2

=400

v=

400

=20 m/s

The speed of stone when it hits the ground will be 20m/s.

hope it will help you ..