Question:
Is Work a scalar or vector quantity?
Answer:
Although work is product of two vectors, it is a scalar quantity.
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.
Name a machine that transforms muscular energy into useful mechanical work.
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.
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 6.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 7.
How does the wind move the blades of a wind-mill ?
Q 8.
When is work done by a force zero ?
Q 9.
What is the form of energy possessed by a running car?
Q 10.
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 11.
What do the machines need for their working ?
Q 12.
Name two forms of mechanical energy.
Q 13.
Name the type of energy possessed by a raised hammer?
Q 14.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 15.
Why do some engines require fuels like petrol and diesel ?
Q 16.
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 17.
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 18.
Name the device which converts electrical energy into mechanical energy.
Q 19.
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 20.
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 21.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
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.
Fill in the blanks :
Ability to do work is called _______.
Q 25.
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 26.
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 27.
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 28.
Is a person doing any work by holding a suitcase ?
Q 29.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 30.
Can a body have energy without having momentum ?
Q 31.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 32.
Fill in the blanks :
A force acting on a body shows a displacement in the direction of the force. It is said _______ is done on the body.
Q 33.
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 34.
Define average power.
Q 35.
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 object by the gravitational force? Explain your answer.
Q 36.
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 37.
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 38.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 39.
How is energy stored in a clock ?
Q 40.
Can a body have energy without possessing momentum?
Q 41.
Fill in the blanks :
If the mass is doubled while its speed remains the same, the kinetic energy will be _____ (be same/double/four times) of the initial kinetic energy.
Q 42.
State the relation between commercial unit of energy and joules.
Q 43.
What is the kinetic energy of an object ?
Q 44.
Name the type of energy possessed by a raised hammer.
Q 45.
Fill in the blanks :
Work done is defined as the product of _____ and ______ in the direction of force.
Q 46.
Assuming the earth revolves around the sun in a perfect circular orbit due to centripetal force exerted by the Sun. Is the work done by the Sun positive or negative.
Q 47.
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 48.
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 49.
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 50.
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.
