Question:
A battery lights a bulb. Describe the energy changes involved in the process.
Answer:
A battery stores chemical energy which transforms into an electrical energy as electric current. The electric current thus lights the bulb (light energy) and bulb also gets warmer (Heat energy). The energy changes involved here are:
Chemical Energy ➼ Electrical Energy ➼ Light Energy + Heat Energy
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 3.
What do the machines need for their working ?
Q 4.
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 5.
How does the wind move the blades of a wind-mill ?
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.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 9.
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 10.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 11.
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 12.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 13.
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 14.
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 15.
When is work done by a force zero ?
Q 16.
What is the form of energy possessed by a running car?
Q 17.
Name two forms of mechanical energy.
Q 18.
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 19.
Name the device which converts electrical energy into mechanical energy.
Q 20.
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 21.
Define average power.
Q 22.
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 23.
Is a person doing any work by holding a suitcase ?
Q 24.
Why do some engines require fuels like petrol and diesel ?
Q 25.
Can a body have energy without having momentum ?
Q 26.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 27.
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 28.
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 29.
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 30.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 31.
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 32.
What is a conservative forces? Give an example.
Q 33.
Name the type of energy possessed by a raised hammer?
Q 34.
A 30g bullet initially travelling at 500 m/s penetrates 12 cm into a wooden block. How much average force does it exerts?
Q 35.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 36.
What do you mean by work ?Give its scientific conception.
Q 37.
When do we say that work is done?
Q 38.
Fill in the blanks :
Work done against a force is stored as _____.
Q 39.
Fill in the blanks :
1 Joule = ____ × ____.
Q 40.
Fill in the blanks :
Kinetic Energy = ½ × _ × _
Q 41.
Fill in the blanks :
If the mass is doubled while its speed remains the same, the kinetic energy will be _____ (be same/double/four times) of the initial kinetic energy.
Q 42.
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 43.
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 44.
From where the falling raindrops gains kinetic energy?
Q 45.
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 46.
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Q 47.
Can there be displacement of an object in the absence of any force acting on it?
Q 49.
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 50.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
