Question:
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
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.
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 4.
What do the machines need for their working ?
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.
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 8.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 9.
When is work done by a force zero ?
Q 10.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 11.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 12.
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 13.
What is the form of energy possessed by a running car?
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 freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
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 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 18.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 19.
Define average power.
Q 20.
Name two forms of mechanical energy.
Q 21.
Can a body have energy without having momentum ?
Q 22.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 23.
Name the type of energy possessed by a raised hammer?
Q 24.
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 25.
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 27.
What do you mean by work ?Give its scientific conception.
Q 28.
The global climate has always fluctuated.Millions of years ago,some parts of the world that are now quite warm, were covered with ice,and over recent centuries,average temperatures have risen and fallen in cycles.What is new,however,is that current and future climate change will be caused not just by natural events but also by activities of human beings.Suggest three simple ways to help save the climate of our planet.
Q 29.
A box is pulled across a floor by applying a force of 100N at an angle of 60 degrees above the horizontal. How much work is done by the applying force in pulling the object to a distance of 8m?
Q 30.
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 31.
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 objjgft by the gravitational force ? Explain your answer.
Q 32.
What are the units of work and energy ?
Q 33.
Is energy a vector quantity ?
Q 34.
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 35.
Identify the kind of energy possessed by a running athlete.
Q 36.
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 37.
A bullet of mass 0.03 kg moving with a speed of 400 m/s penetrates 12 cm into fixed block of wood.Calculate the average force exerted by the wood on the bullet.
Q 38.
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 39.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 40.
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 41.
Define 1 J of work.
Q 42.
Write an expression for kinetic energy of an object
Q 43.
A certain household has consumed 250 units of energy during a month.How much energy is this in joules ?
Q 44.
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 45.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 46.
What do you mean by the law of conservation of energy ?
Q 47.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 49.
Fill in the blanks :
Work done against a force is stored as _____.
Q 50.
Can a body have energy without possessing momentum?
