Answer:
When one-joule work is done in one second by any agent, then its power is said to be one watt. It is the unit of Power.
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.
When is work done by a force zero ?
Q 7.
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 8.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 9.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 10.
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 11.
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 12.
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 13.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 14.
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 15.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 16.
What is the form of energy possessed by a running car?
Q 17.
Name two forms of mechanical energy.
Q 18.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 19.
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 20.
Can a body have energy without having momentum ?
Q 21.
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 22.
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 23.
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 24.
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 25.
Name the device which converts electrical energy into 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.
Define average power.
Q 28.
Is a person doing any work by holding a suitcase ?
Q 29.
Name the type of energy possessed by a raised hammer?
Q 30.
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 31.
Why do some engines require fuels like petrol and diesel ?
Q 32.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 33.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 34.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 35.
From where the falling raindrops gains kinetic energy?
Q 36.
What is a conservative forces? Give an example.
Q 37.
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 38.
How is work done by a force measured ?
Q 39.
What do you mean by the law of conservation of energy ?
Q 40.
When a player hits a football it moves along the curved path and then falls to the ground. Calculate the work done by the force of gravity on the football.
Q 41.
Fill in the blanks :
Work done is positive when the angle between force and displacement is ____ (acute/obtuse)
Q 42.
Fill in the blanks :
Work done by gravity on a falling body is available as ______ (kinetic/potential) energy on reaching the ground.
Q 43.
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 44.
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 45.
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 46.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 47.
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 48.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 49.
Write an expression for kinetic energy of an object
Q 50.
Can there be displacement of an object in the absence of any force acting on it ? Think.Discuss this question with your friends and teacher.
