Question:
Write an expression for the kinetic energy of an object.
Answer:
Let a body of mass m is moving with velocity v then its kinetic energy (K.E.) can be expressed as:
K.E. = ½ mv2
The SI unit of kinetic energy is joules.
DERIVATION: Let a body of mass m is lying stationary on a frictionless horizontal surface. When
a force F acts on it, in time t, it undergoes a displacement S, and it acquires velocity v
If work done W during the process is expressed as:
W = Force × Displacement = F 2kgS
Since F = ma where a is the acceleration.
⇒ W = maS ...(I)
From laws of motion we know that v2- u2= 2aS
Since u = 0, ∴ v2 = 2aS
or aS = ½ mv2
Thus equation (I) becomes,
⇒ W = ½ mv2
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.
Fill in the blanks :
Work done by gravity on a falling body is available as ______ (kinetic/potential) energy on reaching the ground.
Q 6.
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 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.
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 10.
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 11.
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/s
2)
Q 12.
What do you understand by the term energy ? Give its scientific conception.
Q 13.
Two bodies of masses m
1 and m
2 have equal kinetic energies. If p
1 and p
2 are their respective momentum, then ratio p
1 : p
2 is ___?
Q 14.
What are other forms of energies apart from mechanical energy? Does Law of Conservation of Energy apply to all of them?
Q 15.
A battery lights a bulb.Describe the energy changes involved in the process
Q 16.
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 objjgft by the gravitational force ? Explain your answer.
Q 17.
Write an expression for the kinetic energy of an object.
Q 18.
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 19.
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Q 20.
Does the work done on a load depend on the time taken to raise the load?
Q 21.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
Q 22.
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 23.
Define 1 J of work.
Q 24.
What are the units of work and energy ?
Q 25.
Define kinetic energy.Give some examples of bodies possessing kinetic energy.
Q 26.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 27.
What is mechanical energy? What are its types?
Q 28.
Can there be displacement of an object in the absence of any force acting on it?
Q 29.
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 30.
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 increased three times ?
Q 31.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 32.
What is meant by the term potential energy ? Give its two examples.
Q 33.
How do you differentiate between energy and power ?
Q 34.
Fill in the blanks :
Ability of a body to do work due to its position or configuration is known as _________ of the body.
Q 35.
Fill in the blanks :
Work done against a force is stored as _____.
Q 36.
Is it possible that a force acts on a body still the work done is zero? Explain with an example.
Q 37.
Can kinetic energy of an object be negative?
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.
Mathematically show that law of conservation of energy holds true for a free falling object. Consider negligible air resistance.
Q 40.
What is Kilowatt hour?
Q 41.
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 42.
What is the kinetic energy of an object ?
Q 43.
Write an expression for kinetic energy of an object
Q 45.
When is work done by a force positive ?
Q 46.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 47.
Name the type of energy possessed by a raised hammer.
Q 48.
What do you mean by work ?Give its scientific conception.
Q 49.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 50.
Name a few forms of energy and their transformation into each other.
