A body of mass m is allowed to fall with the help of string with downward acceleration g/6 to a distance x . the work done by string is
Answers
Answer:
Explanation: A force of 7N as 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. Wtm is the work done in this case?
Ans. F=7N
s = 8 m
W = F × s
= 7 N × 8 m
W = 56J
∴ Work done is 56 J.
NCERT TEXTBOOK PAGE 149
Q1. When do we say that work is done?
Ans. Work is said to be done when force applied on an object shows the displacement in that object.
W = F x s.
Q2. Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Ans. Work done = W
Force = F
Displacement = s
Work done is equal to the product of the force and displacement.
W = F × s
Q3. Define 1 J of work.
Ans. 1 Joule of work is said to be done when force of 1 Newton acts on a by and shows displacement of 1 metre.
Q4. 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?
Ans. Force = 140 N
s = 15m
W = ?
W = F × s
= 140 N x 15 m
= 2100 Nm
W = 2100 J
∴ Work done in ploughing the length of the field is 2100 J.
NCERT TEXTBOOK PAGE 162
Q1. What is the kinetic energy of an object?
Ans. The energy possessed by an object due to its motion is called kinetic energ of that object.
Where m is mass of the object and v is velocity of the object.
Q2. Write an expression for the kinetic energy of an object.
Q3. The kinetic energy of an object of mass, m moving with a velocity of 5 ms 1 is 25 What will be its kinetic energy when its velocity is doubled? What will be its kine energy when its velocity is increased three times.
NCERT TEXTBOOK PAGE 156
Q1. What is power?
Ans. Power is defined as the rate of work done.
Q2. Define 1 watt of power.
Ans. Power is said to be 1 watt when 1 Joule work is done in 1 second.
Q3. A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Q4. Define average power.
Ans. Average power is defined as the total energy consumed divided by the total time taken.
QUESTIONS FROM NCERT TEXTBOOK
Q1. Look at the activities listed below. Rea sort out, whether or not work is done in the light of your, understanding of the term ‘work’.
(a) Sumo is swimming in a pond
(b) A donkey is carrying a load on its back.
(c) A wind-mill is Itf ding water from a; .well.
(d) A green plant is carrying out photosynthesis
(e) An engine is pulling a train.
(f) Food grains are getting dried in the sun.
(g) A sailboat is moving due to wind energy.
Ans. (a) Suma pushes water in backward direction and’ the displacement is in forward direction, work is said to be done.
W = –ue
(b) Work done is ‘O’
(c) Force ↑↑ Displacement of water W = +ve
(d) No displacement, hence no work is done
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