Class Notes NCERT Solutions for CBSE Students
Question: A body of mass 4 kg initially at rest is subjected to a force of I6 N. What is the kinetic energy acquired by the body at the end of 10 s?
Answer:
Question: A crane pulls up a car weighing 500 kg to a vertical height of 4 m. Calculate the work done by the crane.
Answer: In order to lift the car, the crane has to do work against the force of gravity.
Therefore, the force required = Mg = 500 x 9.8 = 4900 N
Now, displacement undergone by the car, S = 4 m
Hence, work done = FS = 4900 x 4 = 19600 J
Question: A force of 10 N displaces a body by a distance of 2 m at an angle 60° to its own direction. Find the amount of work done.
Answer: By definition, Work = Force x Displacement in the direction of force = FD cos θ
Given, F = 10 N; S = 2m; θ = 60°. Therefore,
W = 10 x 2 x cos 60° = 10 x 2 x 1/2 =10J
Question: A boy of mass 40 kg runs up flight of 50 steps each 10 cm high in 5 seconds. Find: (i) the work done by the boy. (ii) the power developed, (g = 9.8 ms-2)
Answer:
Question: Calculate the power of an engine required to lift 10s kg of coal per hour from a mine 360 m deep, (Take g = 10ms-2).
Answer:
Question: A man whose mass is 50 kg climbs up 30 steps of a stair in 30 s. If each step is 20 cm high, calculate the power used in climbing the stairs. [Take g = 10 ms-2]
Answer:
Question: A mass of 10 kg is dropped from a height of 50 cm. Find its : (i) Kinetic energy (ii) Velocity just as it reaches the ground. Does the velocity depend upon the mass of the particle? Explain. [Take g = 10 ms-2]
Answer:
Question: If you apply 1 J of energy to lift a book of 0.5 kg, how high will it rise? [Take g = 10 ms-2]
Answer: We know that PE = mgh
1 = 0.5 x 10 x h
Therefore, h = 0.2 m = 20 cm
Question: A woman pulls a bucket of water of total mass 5 kg from a well which is 10 m in 10 s. Calculate the power used by her. [Take g = 10 ms-2]
Answer:
Question:
- Define average power.
- A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
- Give the commercial unit of energy in Joules.
Answer:
- Average power is defined as the ratio of total energy consumed to the total time taken.
- P = E/t = 1000/10 = 100 W
- 1 kWh = 3.6 × 106J
