Question:
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Answer:
When a freely falling body eventually stops on reaching the ground,its kinetic energy appears in the form of:
(i) heat (the body and the ground become warmer due to collision),
(ii) sound (produced due to collision of the body with the ground),
(iii) potential energy of configuration of the body and the ground(the body may be deformed and the ground may be depressed at the place of collision).
This process in which the kinetic energy of a freely falling body is lost in an unproductive chain of energy changes is called dissipation of energy.
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.
What do the machines need for their working ?
Q 3.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
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.
What is the form of energy possessed by a running car?
Q 9.
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 10.
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 11.
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 12.
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 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.
Why do some engines require fuels like petrol and diesel ?
Q 16.
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 17.
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 18.
What is the work done by a constant force ?When is it positive,negative or zero ?
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.
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.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 24.
What is Kilowatt hour?
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.
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 28.
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 30.
Define average power.
Q 31.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 32.
What do you understand by the term energy ? Give its scientific conception.
Q 33.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 34.
Name a few forms of energy and their transformation into each other.
Q 35.
What do you mean by the law of conservation of energy ?
Q 36.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 37.
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 38.
Is Work a scalar or vector quantity?
Q 39.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 40.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 41.
A roller coaster is shown in figure, at points i.e. ➊ and ➋, comparatively at what point (i) potential energy is maximum (ii) kinetic energy is maximum
Q 42.
A battery lights a bulb. Describe the energy changes involved in the process.
Q 43.
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 44.
What is the relationship between kinetic energy and work?
Q 45.
Can kinetic energy of an object be negative?
Q 46.
What is a conservative forces? Give an example.
Q 47.
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 48.
What are the various energy transformations that occur when you are riding a bicycle?
Q 49.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 50.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
