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.
How does the wind move the blades of a wind-mill ?
Q 5.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 6.
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 7.
When is work done by a force zero ?
Q 8.
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 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.
What is the form of energy possessed by a running car?
Q 12.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 13.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 14.
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 15.
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 16.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 17.
A motor pump does same amount of water by lifting underground water in shorter time than a hand pump. What do you infer from this statement?
Q 18.
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 19.
A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground.Calculate the work done by him on the luggage.
Q 20.
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 21.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 22.
A man does 200 J of work in 10 s and a boy does 100 J of work in 4 s.(a) Who is delivering more power ?
(b) Find the ratio of the power delivered by the man to that delivered by the boy.
Q 23.
Define average power.
Q 24.
A battery lights a bulb.Describe the energy changes involved in the process
Q 25.
Name two forms of mechanical energy.
Q 26.
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 27.
Can a body have energy without possessing momentum?
Q 28.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 29.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 30.
Fill in the blanks :
Kinetic Energy = ½ × _ × _
Q 31.
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 32.
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 33.
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 object by the gravitational force? Explain your answer.
Q 34.
The magnitude of momentum of a moving object is equal to its kinetic energy. What will be the velocity of the object considering SI units for the system?
Q 35.
What is mechanical energy? What are its types?
Q 36.
From where the falling raindrops gains kinetic energy?
Q 37.
What are the various energy transformations that occur when you are riding a bicycle?
Q 38.
If the momentum of a body is increased
n times, its kinetic energy increases (a) n times (b) 2n times (c) √n times (d) n
2 times
Q 39.
Name the type of energy possessed by a raised hammer?
Q 40.
What is a horsepower?
Q 41.
What is Kilowatt hour?
Q 42.
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 43.
A boy of mass 20 kg climbs up a ladder in 20 seconds. If the height of a ladder is 10 metres, calculate amount of power used.
(Take g = 10 m/s
2)
Q 44.
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 45.
A bullet of mass 0.03 kg moving with a speed of 400 m/s penetrates 12 cm into fixed block of wood.Calculate the average force exerted by the wood on the bullet.
Q 46.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 47.
Write an expression for kinetic energy of an object
Q 48.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 49.
A certain household has consumed 250 units of energy during a month.How much energy is this in joules ?
Q 50.
When is work done by a force positive ?
