Question:
Fill in the blanks :
SI Unit of work is _______.
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.
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.
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 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.
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.
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 12.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 13.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 14.
When is work done by a force zero ?
Q 15.
What is the form of energy possessed by a running car?
Q 16.
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 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.
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 19.
Name two forms of mechanical energy.
Q 20.
Can a body have energy without having momentum ?
Q 21.
Name the device which converts electrical energy into mechanical energy.
Q 22.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 23.
Define average power.
Q 24.
Is a person doing any work by holding a suitcase ?
Q 25.
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 26.
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 27.
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 28.
From where the falling raindrops gains kinetic energy?
Q 29.
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 30.
Is energy a vector quantity ?
Q 31.
Why do some engines require fuels like petrol and diesel ?
Q 32.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 33.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 34.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 35.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
Q 36.
What is a conservative forces? Give an example.
Q 37.
Name the type of energy possessed by a raised hammer?
Q 38.
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 39.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
Q 40.
A battery lights a bulb.Describe the energy changes involved in the process
Q 41.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 42.
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 43.
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 44.
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
Q 45.
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 46.
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 47.
What are the various energy transformations that occur when you are riding a bicycle?
Q 48.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
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.
What is the kinetic energy of an object ?
