Question:
Calculate potential energyof a person having 60 kg mass on the summit of Mt. Everest. Height of Mt. Everest is 8848 m from sea level. (g = 9.8 m/s2)
Answer:
Given mass of the person (m) = 60 kg
Height of the person (h) = 8848 m
Potential Energy possessed by person at the summit = mgh
= 60 × 9.8 × 8848 = 5202624 J = 5.2 × 106 J
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.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 3.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 4.
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 5.
Name a machine that transforms muscular energy into useful mechanical work.
Q 6.
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 7.
How does the wind move the blades of a wind-mill ?
Q 8.
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 9.
What is the form of energy possessed by a running car?
Q 10.
When is work done by a force zero ?
Q 11.
Name two forms of mechanical energy.
Q 12.
Name the device which converts electrical energy into mechanical energy.
Q 13.
What do the machines need for their working ?
Q 14.
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 15.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 16.
Why do some engines require fuels like petrol and diesel ?
Q 17.
Fill in the blanks :
Ability to do work is called _______.
Q 18.
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 19.
Name the type of energy possessed by a raised hammer?
Q 20.
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 21.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 22.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 23.
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 24.
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 25.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 26.
Can there be displacement of an object in the absence of any force acting on it ? Think.Discuss this question with your friends and teacher.
Q 27.
Is a person doing any work by holding a suitcase ?
Q 28.
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 29.
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 30.
Fill in the blanks :
A force acting on a body shows a displacement in the direction of the force. It is said _______ is done on the body.
Q 31.
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 32.
Define average power.
Q 33.
Can a body have energy without having momentum ?
Q 34.
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 35.
A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
Q 36.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 37.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 38.
Two friends Ram and Shyam, each having weight of 40 kg, go for rock climbing. Ram climbs to a height of 3 m in 10 s. and Shyam covers the same height in 12 s. Is the work done by Ram and Shyam equal ? or not ? Compare the power of Ram and Shyam.
Q 40.
Fill in the blanks :
SI Unit of work is _______.
Q 41.
Fill in the blanks :
Work done against a force is stored as _____.
Q 42.
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 43.
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 44.
How is energy stored in a clock ?
Q 46.
Write an expression for the kinetic energy of an object.
Q 47.
Is work a scalar or vector quantity?
Q 48.
From where the falling raindrops gains kinetic energy?
Q 49.
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 50.
whether or not work is done in the light of your understanding of the term ‘work’.
(a) Suma is swimming in a pond.
(b) A donkey is carrying a load on its back.
(c) A wind-mill is lifting 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.
