Question:
A force of 7 N acts on an object.The displacement is,say 8 m,in the direction of the force,[in Fig.].Let us take it that the force acts on the object throughout the displacement What is the work done in this case ?
Answer:
Here,force acting on the object,F=7N
displacement in the direction of the force,s = 8m
Since F acts on the object throughout the displacement,it is constant.Work done by the force, i.e.,
W = F x s = 7N x 8m =
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 3.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 4.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 5.
Define potential energy.Derive an expression for the potential energy of a body of mass m,at a height h above the surface of the Earth.
Q 6.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 7.
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 8.
What do the machines need for their working ?
Q 9.
How does the wind move the blades of a wind-mill ?
Q 10.
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 11.
Name the device which converts electrical energy into mechanical energy.
Q 12.
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 13.
What is the form of energy possessed by a running car?
Q 14.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 15.
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?
Q 16.
Name two forms of mechanical energy.
Q 17.
Fill in the blanks :
Ability to do work is called _______.
Q 18.
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 19.
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 20.
Why do some engines require fuels like petrol and diesel ?
Q 21.
Fill in the blanks :
A stretched rubber band acquires _________(potential/kinetic) energy.
Q 22.
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 23.
A boy of mass 55 kg runs up a flight of 40 stairs,each measuring 0.15 m.Calculate the work done by the boy
Q 24.
A force of 7 N acts on an object.The displacement is,say 8 m,in the direction of the force,[in Fig.].Let us take it that the force acts on the object throughout the displacement What is the work done in this case ?
Q 25.
Is energy a vector quantity ?
Q 26.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 27.
How is energy stored in a clock ?
Q 28.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 29.
Can a body have energy without having momentum ?
Q 31.
Fill in the blanks :
Ability of a body to do work due to its position or configuration is known as _________ of the body.
Q 32.
A spring is stretched, will the work done by the stretching force positive or negative or zero.
Q 33.
Name the type of energy possessed by a raised hammer?
Q 34.
What is a horsepower?
Q 35.
A 30g bullet initially travelling at 500 m/s penetrates 12 cm into a wooden block. How much average force does it exerts?
Q 36.
Define average power.
Q 37.
The velocity of a body moving in a straight line is increased by applying a constant force F,for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.
Q 38.
What is meant by the term potential energy ? Give its two examples.
Q 39.
The global climate has always fluctuated.Millions of years ago,some parts of the world that are now quite warm, were covered with ice,and over recent centuries,average temperatures have risen and fallen in cycles.What is new,however,is that current and future climate change will be caused not just by natural events but also by activities of human beings.Suggest three simple ways to help save the climate of our planet.
Q 40.
A stone of mass 2Kg is tied with a string and is whirled with a centripetal force of 10N in a circular path. How much work is done for making one revolution?
Q 41.
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 is increased three times?
Q 42.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
Q 43.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 44.
What is a conservative forces? Give an example.
Q 45.
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 47.
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 48.
Calculate the power of an engine required to lift 105 kg of coal per hour from a mine 360 m deep.
Q 49.
Is a person doing any work by holding a suitcase ?
