Question

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 .

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?

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

Q4 What kind of energy is possessed by the following :-
a) A stone kept on roof of top.

b) A running car

c) water stored in the reservoir of a dam.

d) A compressed spring

e) A stretched rubber band.

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

Q6 Is work a scaler or vector quantity?
Q7 What is the condition for a force to do work on a body ?

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

Answer 1

$\large\large { \red{\underline{\bf{Question 1) }}}}$

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 = 100kg
• height = 10m
• g = 9.8m/s²

w = Force × distance

w = f × h

w = mgh

$\boxed{\underline{\blue{\textbf{Work done= mgh}}}}$

where,

• m = mass
• g = acceleration due to gravity
• h = height

w = 100 × 10 × 9.8

w = 1000 × 9.8

w = 9800 J

(ii) potential energy of the body at that height

$\boxed{\underline{\blue{\textbf{Potential energy = mgh}}}}$

p = 100 × 10 × 9.8

p = 9800 J

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$\large\large { \red{\underline{\bf{Question 2)}}}}$

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 = 10kg
• height = 5m
• g = 10m/s²
• u = 0
• v = ?

$\boxed{\underline{\blue{\bf{v^{2}= u^{2}+ 2gh}}}}$

v² = 0 + 2 × 10 × 5

v² = 10 × 10

v = √100

v = 10m/s

$\boxed{\underline{\blue{\bf{K.E= \frac{1}{2}mv^{2}}}}}$

= 1/2 × 10 × 10²

= 5 × 10 × 10

= 500J

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$\large\large { \red{\underline{\bf{Question 3) }}}}$

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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$\large\large { \red{\underline{\bf{Question 4) }}}}$

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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$\large\large { \red{\underline{\bf{Question 5) }}}}$

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

Solution :

• mass = 50 kg
• Kinetic energy = 625 J

$\boxed{\underline{\blue{\bf{K.E= \frac{1}{2}mv^{2}}}}}$

625 = 1/2 × 50 × v²

625 = 25 × v²

625/25 = v²

v = √25

v = 5m/s

So,

$\green{\textrm{ The man should run with the speed of 5m/s}}$

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$\large\large { \red{\underline{\bf{Question 6) }}}}$

Q6 Is work a scaler or vector quantity?

Answer - work is a scaler quantity

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$\large\large { \red{\underline{\bf{Question 7) }}}}$

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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$\large\large { \red{\underline{\bf{Question 8) }}}}$

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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