Question:
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
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.
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 16.
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 17.
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 18.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 19.
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 20.
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 21.
What is a horsepower?
Q 22.
What is Kilowatt hour?
Q 23.
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 24.
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 25.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 26.
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 27.
Write an expression for kinetic energy of an object
Q 28.
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 29.
Define average power.
Q 30.
A battery lights a bulb.Describe the energy changes involved in the process
Q 31.
A certain household has consumed 250 units of energy during a month.How much energy is this in joules ?
Q 32.
Name two forms of mechanical energy.
Q 33.
Name the device which converts electrical energy into mechanical energy.
Q 34.
What is the difference between potential energy and kinetic energy ?
Q 35.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 36.
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 37.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 38.
A stone of mass 2Kg is tied with a string and is whirled with a centripetal force of 10N in a circular path. How much work is done for making one revolution?
Q 39.
Fill in the blanks :
Work done against a force is stored as _____.
Q 40.
A force of 10 N moves a body with a constant speed of 2 m/s. Calculate the power of the body.
Q 41.
Can a body have energy without possessing momentum?
Q 42.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 43.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 44.
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 45.
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 46.
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 47.
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 48.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
Q 49.
Fill in the blanks :
Kinetic Energy = ½ × _ × _
Q 50.
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
