Physics

Work and Energy

Question:

Define power.

Answer:

The rate at which work is done by a force is called power. Work done per unit time is called power.

Power = Work(W) ÷ Time (T)
The SI unit of power is Watt. 1 Watt = 1 J per second.

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Work and Energy

Q 1.

Fill in the blanks :
Work is a ______ (scalar/vector) quantity.

Q 2.

Fill in the blanks :
Work done on an object is _____ if displacement is zero.

Q 3.

A force of 10 N moves a body with a constant speed of 2 m/s. Calculate the power of the body.

Q 4.

A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?

Q 5.

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 6.

Calculate potential energyof a person having 60 kg mass on the summit of Mt. Everest. Height of Mt. Everest is 8848 m from sea level. (g = 9.8 m/s2)

Q 7.

Fill in the blanks :
Work done is defined as the product of _____ and ______ in the direction of force.

Q 8.

Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)

Q 9.

Identify the kind of energy possessed by a running athlete.

Q 10.

Fill in the blanks :
Work done by gravity on a falling body is available as ______ (kinetic/potential) energy on reaching the ground.

Q 11.

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 12.

An object of mass m is raised from the the earth to an height of equal to the radius of the earth (R). Calculate the gain in potential energy by the object. Assume gravity of the earth is g.

Q 13.

A spring is stretched, will the work done by the stretching force positive or negative or zero.

 
 

Q 14.

Fill in the blanks :
SI Unit of work is _______.

Q 15.

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 16.

What is the relationship between kinetic energy and work?

Q 17.

A man exerts a force of 200 N in pulling a cart at a constant speed of 16 m/s.Calculate the power spent by the man.

Q 18.

What do you understand by the term energy ? Give its scientific conception.

Q 19.

What do you mean by the law of conservation of energy ?

Q 20.

When do we say that work is done?

Q 21.

Fill in the blanks :
A form of energy an object has because of its motion is called ________.

Q 22.

A pendulum of length 1m and with a bob of mass 1 kg swings in a vertical plane. Find the work done (from the below said choices) by weight of the bob when it moves from position A to B (as shown in figure). (Take g = 10 m/sec^2)


a. 4J
b. -4J
c. -5 J
d. 5 J

Q 23.

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 24.

What are other forms of energies apart from mechanical energy? Does Law of Conservation of Energy apply to all of them?

Q 25.

Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.

Q 26.

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 27.

Define 1 J of work.

Q 28.

What are the various energy transformations that occur when you are riding a bicycle ?

Q 29.

Is work a scalar quantity or a vector quantity ?

Q 30.

What are the units of work and energy ?

Q 31.

Is energy a vector quantity ?

Q 32.

What do you mean by work ?Give its scientific conception.

Q 33.

Define kinetic energy.Give some examples of bodies possessing kinetic energy.

Q 34.

What do you mean by power of an agent ? Give an expression for power.

Q 35.

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 36.

In physics,energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems.However,this must be understood as an overly simplified definition as we shall come to know in higher classes that not all energy can perform work.
(a) How did the concept of energy emerge ?
(b) How much electric energy is generated in a typical lightning strike ? What are the forms to which this energy gets converted ?
(c) What is the kinetic energy of a passenger seated in a moving plane :(i) with respect to the plane (ii) with respect to the Earth.

Q 37.

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 38.

Fill in the blanks :
The sum of P.E. and K.E. is called __________.

Q 39.

A battery lights a bulb. Describe the energy changes involved in the process.

 
 

Q 40.

What is mechanical energy? What are its types?

Q 41.

What is a conservative forces? Give an example.

Q 42.

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 43.

Name the type of energy possessed by a raised hammer?

Q 44.

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 45.

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

Q 46.

Give examples for the following scenarios of energy transformations. You may choose the answer(s) from the following list of words

solar cell, turbine, mixer, fan, steam engine, automobiles, green plants, nuclear reactor, electric bulb, torch, electric bulb, microphone, loudspeaker, geyser, heater, car battery, inverter, LPG

 

SNo.    Energy Transformation
From ⟶ To
     Give Example
1. Mechanical ⟶ Electrical          _________
2. Electrical ⟶ Mechanical      _________
3. Electrical ⟶ Heat      _________
4. Heat ⟶ Mechanical      _________
5. Electrical ⟶ Light      _________
6. Electrical ⟶ Sound      _________
 
7. Chemical ⟶ Heat      _________
8. Electrical ⟶ Chemical      _________
9. Sound ⟶ Electrical      _________
10. Chemical ⟶ Electrical      _________
11. Light ⟶ Electric      _________
12. Chemical ⟶ Mechanical      _________
13. Nuclear ⟶ Electrical      _________
14. Light ⟶ Chemical      _________

Q 47.

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 48.

What is a horsepower?

Q 49.

What is Kilowatt hour?

Q 50.

A certain household has consumed 250 units of energy during a month. How much energy is this in joules?