Q1A body of mass 100kg is lifted up by 10m .

(i) the amount of work done.

(ii) potential energy of the body at that height .

answer

(i) the amount of work done.

mass = 100kgheight = 10mg = 9.8m/s²

w = Force × distance

w = f × h

w = mgh

where,

m = massg = acceleration due to gravityh = height

w = 100 × 10 × 9.8

w = 1000 × 9.8

w = 9800 J

(ii) potential energy of the body at that height

p = 100 × 10 × 9.8

p = 9800 J

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Q2 A man drops a 10kg rock from the top of a 5m ladder . what is it's speed just before it hits the ground? ( g = 10m/s²)

Solution :

mass = 10kgheight = 5mg = 10m/s²u = 0v = ?

v² = 0 + 2 × 10 × 5

v² = 10 × 10

v = √100

v = 10m/s

= 1/2 × 10 × 10²

= 5 × 10 × 10

= 500J

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Q3 what happens to the potential energy of a body When its height is doubled?

answer :

If the potential energy of a body is doubled the potential energy is Also doubled.

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Q4 What kind of energy is possessed by the following :-

a) A stone kept on roof of top.

answer - potential energy

b) A running car

answer - kinetic energy

c) water stored in the reservoir of a dam.

answer - potential Energy

d) A compressed spring

answer - potential Energy

e) A stretched rubber band.

answer - Potential Energy

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Q5 How fast should a man of 50kg run so that his kinetic energy be 625J

Solution :

mass = 50 kgKinetic energy = 625 J

625 = 1/2 × 50 × v²

625 = 25 × v²

625/25 = v²

v = √25

v = 5m/s

So,

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Q6 Is work a scaler or vector quantity?

answer - work is a scaler quantity

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Q7 What is the condition for a force to do work on a body ?

answer :- Displacement is the condition for a force to do work on a body.

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Q8 On what factors does the kinetic energy of a body depends?

answer :

Kinetic Energy of a body depends on its mass and velocity , therefore heavy bodies moving with high velocities have more kinetic energy, than slow moving bodies of small mass.

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