Question:
What is Kilowatt hour?
Answer:
Kilo watt hour is a unit of energy. It define the relation between work and power. 1 kW hour means one killowatt of power is supplied for an hour.
⇒ 1 kWh = 1000J/s × 3600 s = 3.6 × 106 J
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
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 3.
What do the machines need for their working ?
Q 4.
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 5.
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 6.
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 7.
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 8.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 9.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 10.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 11.
How does the wind move the blades of a wind-mill ?
Q 12.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 13.
Define average power.
Q 14.
When is work done by a force zero ?
Q 15.
Name two forms of mechanical energy.
Q 16.
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 17.
Many people debate about whether there is a God,or what God is.Is God an individual personality,sitting up in heaven listening to and granting our requests,or is God simply all the energy that exists in the Universe,or is God simply nature or the laws of nature ?
Q 18.
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 19.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 20.
What are the units of work and energy ?
Q 21.
Name the type of energy possessed by a raised hammer.
Q 22.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 23.
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
Q 24.
Name the type of energy possessed by a raised hammer?
Q 25.
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 26.
A force of 5 N is acting on an object.The object is displaced through 2 m in the direction of the force.[in Fig.].If the force acts all through the displacement,find the work done by the force.
Q 27.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
Q 28.
Define 1 W of power.
Q 29.
How is work done by a force measured ?
Q 30.
Is energy a vector quantity ?
Q 31.
Name a few forms of energy and their transformation into each other.
Q 32.
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 33.
A force of 10 N moves a body with a constant speed of 2 m/s. Calculate the power of the body.
Q 34.
Fill in the blanks :
Work done by gravity on a falling body is available as ______ (kinetic/potential) energy on reaching the ground.
Q 35.
A battery lights a bulb. Describe the energy changes involved in the process.
Q 36.
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 37.
What is the form of energy possessed by a running car?
Q 38.
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 39.
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 40.
What do you understand by the term energy ? Give its scientific conception.
Q 41.
Can a body have energy without having momentum ?
Q 42.
When do we say that work is done?
Q 43.
Is Work a scalar or vector quantity?
Q 44.
A box is pulled across a floor by applying a force of 100N at an angle of 60 degrees above the horizontal. How much work is done by the applying force in pulling the object to a distance of 8m?
Q 45.
A boy of mass 45 kg climbs up 20 steps in 20 second. If each step is 25 cm high, calculate the power used in climbing
Q 46.
When a player hits a football it moves along the curved path and then falls to the ground. Calculate the work done by the force of gravity on the football.
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 :
An object moving in a circular orbit. The work done by the centrepetal force acting on the object is ______ (zero/non-zero).
Q 50.
Write an expression for the kinetic energy of an object.
