Question:
What do you mean by kinetic energy ? Derive an expression for the kinetic energy of an object of mass m moving with velocity,v.
Answer:
Refer to Art. 5.5,Page 264; Art. 5.6,Page 265.
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.
What do the machines need for their working ?
Q 4.
How does the wind move the blades of a wind-mill ?
Q 5.
Name a machine that transforms muscular energy into useful mechanical work.
Q 6.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 7.
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 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.
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 10.
What is the form of energy possessed by a running car?
Q 11.
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 12.
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 13.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 14.
Name two forms of mechanical energy.
Q 15.
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 16.
Why do some engines require fuels like petrol and diesel ?
Q 17.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 18.
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 19.
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 20.
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 21.
Is a person doing any work by holding a suitcase ?
Q 22.
Fill in the blanks :
Ability to do work is called _______.
Q 23.
What is Kilowatt hour?
Q 24.
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 25.
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 objjgft by the gravitational force ? Explain your answer.
Q 26.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 27.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 28.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 29.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 30.
What is the relationship between kinetic energy and work?
Q 31.
Can kinetic energy of an object be negative?
Q 32.
What do you understand by the term energy ? Give its scientific conception.
Q 33.
The recent horrific storm surge flooding New Jersey and New York in US by Hurricane Sandy was almost prefectly predicted well in advance,but was more extreme than the average person might expect from a minimal hurricane.There is a metric that quantifies the energy of a storm based on how far out tropical-storm force winds extend from the centre,known as Integrated Kinetic Energy (IKE).
(i) What is Sandy’s ranking in terms of IKE among all the hurricanes witnessed so far?
(ii) What is the IKE of Sandy?
(iii) How was Sandy different from Hurricane Katrina ?
(iv) Which human value did Sandy generate among the people round the globe?
Q 34.
Does the work done on a load depend on the time taken to raise the load?
Q 35.
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 36.
What are the various energy transformations that occur when you are riding a bicycle?
Q 37.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 38.
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 39.
Calculate the power of an engine required to lift 105 kg of coal per hour from a mine 360 m deep.
Q 41.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 42.
An electric heater is rated 1500 W.How much energy does it use in 10 hours ?
Q 43.
How is energy stored in a clock ?
Q 44.
Name a few forms of energy and their transformation into each other.
Q 45.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 46.
Fill in the blanks :
SI Unit of work is _______.
Q 47.
Fill in the blanks :
Work done on an object is _____ if displacement is zero.
Q 48.
Fill in the blanks :
Work done is positive when the angle between force and displacement is ____ (acute/obtuse)
Q 49.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
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 is increased three times?
