Question

An object is falling from the height of 1 km . The mass of that object is 20 g .

Find :

(i) Time taken to reach at the ground

(ii) Potential energy

(iii) Kinetic energy

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Answer 1

• An object is falling from the height of 1 k.m .

• The mass of that object is 20g .

(i) Height = 1/2 × g × t²

→ 1000 = 1/2 × 10 × t²

→ 1000 = 5 × t²

→ t² = 1000/5

→ t = √200

→ t = 10√2 s

(ii) Potential energy will be zero . Because when the body is released from a height of 1 k.m then all the potential energy will be converted to kinetic energy .

(iii) Kinetic energy = mgh

→ Kinetic energy = 20/1000 × 10 × 1000

→ Kinetic energy = 0.02 × 10⁴

→ Kinetic energy = 0.2 × 10³ J

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Answer 2

Answer:

Explanation:

i ) the time taken to reach earth do not depend on mass

As initial velocity is zero ,

Using h = ut + 1/2 gt^2

1000 m = 1/2 ( 10 ) t^2

t^2= 1000/5 = 200

So , t=10√2 s

ii) potential energy ( at top ) = mgh

P.E. = (20/1000) * 10 * 1000

= 200 joule

{at the end , P.E. will be zero}

{at top , K.E is zero }

iii) kinetic energy =1/2 mv^2

→ velocity ( v ) just before hitting ground

V = u + gt

V = 10* 10√2 = 100√2 ms^-²

K.E. = (1/2)*(20/1000)(100√2)²

= 200 joule