Question:
An electric bulb of 60 W is used for 6 h per day.Calculate the ‘units’ of energy consumed in one day by the bulb
Work and Energy
Q 1.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 2.
Name a machine that transforms muscular energy into useful mechanical work.
Q 3.
How do you differentiate between energy and power ?
Q 4.
A coolie carries a load of 50 kg on his head and walks on a level road upto 100 m.What is the work done by him ?
Q 5.
What do you mean by work ?Give its scientific conception.
Q 6.
Define kinetic energy.Give some examples of bodies possessing kinetic energy.
Q 7.
A spring is stretched, will the work done by the stretching force positive or negative or zero.
Q 8.
Is work a scalar or vector quantity?
Q 9.
Assuming the earth revolves around the sun in a perfect circular orbit due to centripetal force exerted by the Sun. Is the work done by the Sun positive or negative.
Q 10.
Write an expression for the kinetic energy of an object in terms (i) velocity (
v) of an object (ii) in terms of momentum (
p) of an object.
Q 11.
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
Q 12.
What is the relationship between kinetic energy and work?
Q 13.
Certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done by the force.
Q 14.
Can kinetic energy of an object be negative?
Q 15.
What is mechanical energy? What are its types?
Q 16.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 17.
From where the falling raindrops gains kinetic energy?
Q 18.
A person throws a stone of mass 3kg. It crosses the top of a wall of 2m high at a speed of 4m/s. What is the total mechanical energy possessed by the stone when it crosses the wall?(Take g = 10 m/s)
Q 19.
Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
Q 20.
If the momentum of a body is increased
n times, its kinetic energy increases (a) n times (b) 2n times (c) √n times (d) n
2 times
Q 21.
Name the type of energy possessed by a raised hammer?
Q 22.
Identify the kind of energy possessed by a running athlete.
Q 23.
Mathematically show that law of conservation of energy holds true for a free falling object. Consider negligible air resistance.
Q 24.
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Q 25.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 26.
Can there be displacement of an object in the absence of any force acting on it?
Q 28.
A motor pump does same amount of water by lifting underground water in shorter time than a hand pump. What do you infer from this statement?
Q 29.
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Q 30.
State the relation between commercial unit of energy and joules.
Q 31.
A body of mass 15 kg undergoes downward displacement of 40m under the effect of gravitational force. How much work is done? (take g = 10 m/s
2)
Q 32.
A body of mass 120 g is taken vertically upwards to reach the height of 5m. Calculate work done. (Take g = 10 m/s
2)
Q 33.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 34.
A 30g bullet initially travelling at 500 m/s penetrates 12 cm into a wooden block. How much average force does it exerts?
Q 35.
A boy of mass 20 kg climbs up a ladder in 20 seconds. If the height of a ladder is 10 metres, calculate amount of power used.
(Take g = 10 m/s
2)
Q 36.
A force of 5 N is acting on an object.The object is displaced through 2 m in the direction of the force.[in Fig.].If the force acts all through the displacement,find the work done by the force.
Q 37.
A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground.Calculate the work done by him on the luggage.
Q 38.
An object of mass 15 kg is moving with a uniform velocity of 4 m/s.What is the kinetic energy possessed by the object ?
Q 39.
A bullet of mass 0.03 kg moving with a speed of 400 m/s penetrates 12 cm into fixed block of wood.Calculate the average force exerted by the wood on the bullet.
Q 40.
The mass of a ball A is double the mass of another ball B.The ball A moves at half the speed of the ball B.Calculate the ratio of the kinetic energy of A to the kinetic energy of B.
Q 41.
A bullet of mass 20 g is found to pass two points 30 m apart in 4 s ? Assuming the -speed to be constant,find its kinetic energy.
Q 42.
Two girls,each of weight 400 N,climb up a rope through a height of 8 m.We name one of the girls A and the other B.Girl A takes 20 s while B takes 50 s to accomplish this task.What is the power expended by each girl ?
Q 43.
A boy of mass 50 kg runs up a staircase of 45 steps in 9 s.If the height of each step is 15 cm,find his power.Take g =
.
Q 44.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 45.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 46.
A man exerts a force of 200 N in pulling a cart at a constant speed of 16 m/s.Calculate the power spent by the man.
Q 47.
A man does 200 J of work in 10 s and a boy does 100 J of work in 4 s.(a) Who is delivering more power ?
(b) Find the ratio of the power delivered by the man to that delivered by the boy.
Q 48.
What is the kinetic energy of an object ?
Q 49.
Write an expression for kinetic energy of an object
Q 50.
The kinetic energy of an object of mass,m moving with a velocity of 5 m/s is 25 J.What will be its kinetic energy when its velocity is doubled ? What will be its kinetic energy when its velocity increased three times ?
