Work and Energy NCERT in-text questions
Table of Contents
Work and Energy NCERT in-text questions page 148
Question 1:
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?
Ans: Force applied on the body in the direction of displacement = 7N
Displacement in direction of force = 8m
Formula/concept: Work done when force and displacement are in the same direction = Force × Displacement
Work done = Force × Displacement = 7 × 8 = 56J
Work and Energy NCERT in-text questions page 149
Question 1:
When do we say that work is done?
Answer: Work is said to be done if force is applied to the body and it displaces in the direction of the applied force.
Question 2:
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Answer: Work done = Force × Displacement
Question 3:
Define 1 J of work.
Answer: If F = 1 N, Displacement = 1m
Work done = Force × Displacement = 1N × 1m = 1Nm = 1J
If one newton of force is applied to the body and it displaces in the direction of the applied force by 1 m, then it is said that one joule of work is done.
Question 4:
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Answer: Force = 140N, Displacement = 15m
Work done = Force × Displacement = 140N × 15m = 2100Nm = 2100J
Work and Energy NCERT in-text questions page 152
1. What is the kinetic energy of an object?
Answer: The energy possessed by a body due to its motion is called kinetic energy.
2. Write an expression for the kinetic energy of an object.
Ans: Expression for the kinetic energy of an object KE (K) = ½ mv2
3. The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Work and Energy NCERT in-text questions page 156
Question 1:
What is power?
Ans: The rate of doing work is called power.
Power = Work / Time
Question 2:
Define 1 watt of power.
Ans: The power of an electrical appliance is said to be one watt if it consumes or produces one joule of energy in one second.
Question 3:
3. A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Answer: Power = Work / Time = Electrical Energy / Time = 1000J / 10s = 100 J/s = 100 watt
Question 4:
4. Define average power.
Answer: The ratio of total work done (total energy consumed or produced) to total time taken is called the average power.
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