Question:
A spring is stretched, will the work done by the stretching force positive or negative or zero.
Answer:
Since the displacement of the stretched force and the force are acting in the same direction the angle between them becomes zero. So the work done will be positive.
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.
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.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
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.
Name a machine that transforms muscular energy into useful mechanical work.
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.
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.
Name two forms of mechanical energy.
Q 13.
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 14.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 15.
Why do some engines require fuels like petrol and diesel ?
Q 16.
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 17.
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 18.
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 19.
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 20.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 21.
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 22.
Is a person doing any work by holding a suitcase ?
Q 23.
Name the device which converts electrical energy into mechanical energy.
Q 24.
Fill in the blanks :
Ability to do work is called _______.
Q 25.
Can a body have energy without having momentum ?
Q 26.
When is work done by a force zero ?
Q 27.
Name the type of energy possessed by a raised hammer?
Q 28.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 29.
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.
What is the kinetic energy of an object ?
Q 31.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 32.
Is energy a vector quantity ?
Q 33.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 34.
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 35.
Write an expression for kinetic energy of an object
Q 36.
What do you understand by the term energy ? Give its scientific conception.
Q 37.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 38.
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.
Fill in the blanks :
Work done against a force is stored as _____.
Q 41.
Fill in the blanks :
Work done is defined as the product of _____ and ______ in the direction of force.
Q 42.
Fill in the blanks :
An object moving in a circular orbit. The work done by the centrepetal force acting on the object is ______ (zero/non-zero).
Q 43.
Is work a scalar or vector quantity?
Q 44.
A battery lights a bulb. Describe the energy changes involved in the process.
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.
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 47.
What is a conservative forces? Give an example.
Q 48.
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 49.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
