The comprehensive approach in Kerala Syllabus 9th Standard Physics Notes Pdf Chapter 6 Work and Energy Notes Extra Questions and Answers ensures conceptual clarity.
Kerala Syllabus Std 9 Physics Chapter 6 Work and Energy Extra Questions and Answers
Question 1.
Classify the following into work done and work is not done
- A mango falling from a mango tree
- Pushing a table while sitting on it
- Pushing a wall
- Kicking a football
- A trolley is moving forward
- Standing with a load above the head
Answer:
Work done:
- A mango falling from a mango tree
- Kicking a football
- A trolley is moving forward
Work is not done
- Pushing a table while sitting on it
- Pushing a wall
- Standing with a load above the head
Question 2.
What are the factors on which work done depends upon?
Answer:
Force, displacement
Question 3.
When Lekshmi applies a force of 50 N on an object, It undergoes a displacement of 2m. When Vinitha applied the same force, it undergoes a displacement of 3m if so,
a) Which person has done more work
b) Give a reason
c) Calculate the work done by each person
Answer:
a) Vinitha
b) Displacement is greater
c) Work done by Lekshmi
W = Fs = 50N × 2m =100 J
Work done by Vineetha
W = Fs = 50N × 3 = 150J
Question 4.
Calculate work done when a boy of mass 40 kg climbs a staircase of height 50 cm, g = 1o m/s2.
Answer:
W = Fs
F = mg = 40 × 10 = 400N
s = h = 0.5 m
W = 400 × 0.5 = 200 J
Question 5.
Fill in the blanks
a) Work done when a body of mass 100 g is lifted up to a height 1 metre is _____
b) 1 HP = ______watt
Answer:
a) 1 J
b) 746 W
Question 6.
a) What is meant by kinetic energy?
b) How do mass and velocity affect kinetic energy?
c) A body of mass 20 kg is moving with a velocity of 5 m/s. Calculate the kinetic energy.
Answer:
a) The energy possessed by a body by virtue of its motion is called kinetic energy.
b) As ma.s increases, kinetic energy increases. When mass is doubled, kinetic energy is also doubled. As velocity increases, kinetic energy increases, velocity is doubled kinetic energy becomes four times.
c) Kinetic energy K = \(\frac{1}{2}\) mv2 = \(\frac{1}{2}\) × 20 × 52 = 250 J
Question 7.
State law of conservation of energy.
Answer:
Energy can neither be created nor be destroyed. It can be transformed from one form to another.
Question 8.
From what you have learnt of potential energy and kinetic energy, Write down the form of energy possessed by the bodies given below.
a) Water in a dam
b) Stretched rubber band
c) Mango falling from a tree
Answer:
a) Potential energy
b) Potential energy
c) Potential energy and Kinetic energy
Question 9.
Calculate the potential energy of a stone of mass 40 kg at a height 12 m
Answer:
U = mgh
= 40 × 10 × 12 = 4800 J
Question 10.
Write situations in which potential energy vanes.
Answer:
- Climbing a ladder
- Falling of a coconut
- Pumping water to a tank at a height
- Rising of a kite
- Falling of a flower pot from a sunshade
Question 11.
a) What is power?
b) The time taken to move an object at a distance of 5m is 10 s. If the force applied is 30 N, what is the power?
Answer:
a) The rate of doing work is power
b) s = 5m, t = 10 s, F = 30N
W = Fs = 30 × 5 = 150 J
t = 10 s
Power P = \(\frac{w}{t}\) = \(\frac{150}{60}\) = 15 w
Question 12.
If a man of mass 50 kg takes 60 s to climb up 20 steps, each 15 cm high, calculate his power.
Answer:
m = 50 kg, g = 10 m/s2
h = 15 cm × 20 = 300 cm = 3m
t = 60 s
work W = mgh = 50 × 10 × 3 = 1500 J
Power p = \(\frac{w}{t}\) = \(\frac{1500}{60}\) = 25 w
Question 13.
A boy of mass 50kg can climb a mountain of height 30 m in 5 minutes. What will be his power?
Answer:
P = \(\frac{mgh}{t}\) = \(\frac{50 \times 10 \times 30}{5 \times 60}\) = 50 w
Question 14.
A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Answer:
W = 1000 J, t = 10 s
Power p = \(\frac{w}{t}\) = \(\frac{1000}{10}\) = 100 w
Question 15.
State the relation between kW h and joule. Define 1 watt.
Answer:
1 kWh = 1000 Wh = 1000 Js-1 × 60 × 60 s = 3.6 × 106 J
1 watt is the power of an agent that can do one joule of work in one second.