Question:
What is a horsepower?
Answer:
A horsepower (hp) is another unit of power. 1 hp = 746 Watts
Work and Energy
Q 1.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 2.
Name a machine that transforms muscular energy into useful mechanical work.
Q 3.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 4.
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 5.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 6.
What do the machines need for their working ?
Q 7.
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 8.
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 9.
How does the wind move the blades of a wind-mill ?
Q 10.
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 11.
Name the device which converts electrical energy into mechanical energy.
Q 12.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 13.
Why do some engines require fuels like petrol and diesel ?
Q 14.
What is the form of energy possessed by a running car?
Q 15.
Name two forms of mechanical energy.
Q 16.
Fill in the blanks :
Ability to do work is called _______.
Q 17.
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 18.
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 19.
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 20.
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 21.
Can a body have energy without having momentum ?
Q 22.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
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.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 25.
Fill in the blanks :
A stretched rubber band acquires _________(potential/kinetic) energy.
Q 26.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 27.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 28.
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.
Q 29.
How is energy stored in a clock ?
Q 30.
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 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.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 36.
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 37.
Fill in the blanks :
Kinetic Energy = ½ × _ × _
Q 38.
A spring is stretched, will the work done by the stretching force positive or negative or zero.
Q 39.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 40.
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 41.
Define 1 W of power.
Q 42.
Define average power.
Q 43.
When is work done by a force zero ?
Q 44.
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 45.
Fill in the blanks :
Ability of a body to do work due to its position or configuration is known as _________ of the body.
Q 46.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 47.
Calculate the amount of work done in drawing a bucket of water weighing 10kg from a well of depth 20m.
Q 48.
A boy of mass 45 kg climbs up 20 steps in 20 second. If each step is 25 cm high, calculate the power used in climbing
Q 49.
Two friends Ram and Shyam, each having weight of 40 kg, go for rock climbing. Ram climbs to a height of 3 m in 10 s. and Shyam covers the same height in 12 s. Is the work done by Ram and Shyam equal ? or not ? Compare the power of Ram and Shyam.
Q 50.
Is it possible that a force acts on a body still the work done is zero? Explain with an example.
