Question:
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
Answer:
Negative work. The force which holds the stone is applied in upward direction while the displacement occurs in the downward direction (? = 180°).
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.
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.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
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.
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.
Is a person doing any work by holding a suitcase ?
Q 20.
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 21.
Fill in the blanks :
Ability to do work is called _______.
Q 22.
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 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.
Fill in the blanks :
Work done is positive when the angle between force and displacement is ____ (acute/obtuse)
Q 25.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 26.
Define potential energy? What are different types of potential energy?
Q 27.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 28.
Can there be displacement of an object in the absence of any force acting on it?
Q 30.
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 31.
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
Q 32.
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 33.
How is work done by a force measured ?
Q 34.
Name the device which converts electrical energy into mechanical energy.
Q 35.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 36.
What do you mean by the law of conservation of energy ?
Q 37.
How do you differentiate between energy and power ?
Q 38.
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 40.
Fill in the blanks :
Work done against a force is stored as _____.
Q 41.
Fill in the blanks :
SI Unit of work is _______.
Q 42.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 43.
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 44.
A spring is stretched, will the work done by the stretching force positive or negative or zero.
Q 45.
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 46.
Can kinetic energy of an object be negative?
Q 47.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 48.
What is a conservative forces? Give an example.
Q 49.
What are other forms of energies apart from mechanical energy? Does Law of Conservation of Energy apply to all of them?
Q 50.
Name the type of energy possessed by a raised hammer?
