Question:
What do you mean by work ?Give its scientific conception.
Answer:
Refer to Art. 5.2,Page 259.
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.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 3.
How does the wind move the blades of a wind-mill ?
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.
What is the form of energy possessed by a running car?
Q 6.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
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.
Name a machine that transforms muscular energy into useful mechanical work.
Q 9.
What do the machines need for their working ?
Q 10.
Name two forms of mechanical energy.
Q 11.
Why do some engines require fuels like petrol and diesel ?
Q 12.
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 13.
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 14.
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 15.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 16.
Name the device which converts electrical energy into mechanical energy.
Q 17.
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 18.
Is a person doing any work by holding a suitcase ?
Q 19.
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 20.
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 21.
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 22.
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 23.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 24.
Name the type of energy possessed by a raised hammer?
Q 25.
When is work done by a force zero ?
Q 26.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 27.
Can a body have energy without having momentum ?
Q 28.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 29.
Fill in the blanks :
Ability to do work is called _______.
Q 30.
Define average power.
Q 31.
Fill in the blanks :
Work done against a force is stored as _____.
Q 32.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 33.
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 34.
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 35.
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 36.
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 37.
What is meant by the term potential energy ? Give its two examples.
Q 38.
The recent horrific storm surge flooding New Jersey and New York in US by Hurricane Sandy was almost prefectly predicted well in advance,but was more extreme than the average person might expect from a minimal hurricane.There is a metric that quantifies the energy of a storm based on how far out tropical-storm force winds extend from the centre,known as Integrated Kinetic Energy (IKE).
(i) What is Sandy’s ranking in terms of IKE among all the hurricanes witnessed so far?
(ii) What is the IKE of Sandy?
(iii) How was Sandy different from Hurricane Katrina ?
(iv) Which human value did Sandy generate among the people round the globe?
Q 39.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 40.
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 42.
State the relation between commercial unit of energy and joules.
Q 43.
Is energy a vector quantity ?
Q 44.
Name a few forms of energy and their transformation into each other.
Q 45.
What do you mean by the law of conservation of energy ?
Q 46.
What do you mean by power of an agent ? Give an expression for power.
Q 47.
How do you differentiate between energy and power ?
Q 48.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 49.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 50.
Fill in the blanks :
A force acting on a body shows a displacement in the direction normal to the direction of the force. It is said _______ done on the body.
