Question:
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.
Answer:
1. Drive less.Walk,Carpool or take Public Transport.You will save emission of 1.5 kg of for every 5 km you do not drive.
2.Use renewable energy.Use solar water heater instead of an electric geyser.A 100 litre solar water heater can save around 1500 units of electricity every year.For lighting,use batteries that can be charged by sunlight.A solar cooker cooks food without losing its essential nutrients.
3.Check your tyres.Keeping your tyres properly inflated improves the fuel efficiency of your vehicle.Every litre of petrol saved,keeps 2.5 kg out of atmosphere.Using radial tyres will help you save 3% to 7% of fuel.
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
What do the machines need for their working ?
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.
How does the wind move the blades of a wind-mill ?
Q 5.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
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.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 8.
When is work done by a force zero ?
Q 9.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 10.
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 11.
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 12.
What is the form of energy possessed by a running car?
Q 13.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 14.
Name two forms of mechanical energy.
Q 15.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
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.
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 18.
Can a body have energy without having momentum ?
Q 19.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 20.
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 21.
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 22.
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 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.
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 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 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 27.
Write an expression for kinetic energy of an object
Q 28.
A battery lights a bulb.Describe the energy changes involved in the process
Q 29.
Is energy a vector quantity ?
Q 30.
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 31.
From where the falling raindrops gains kinetic energy?
Q 32.
Name the type of energy possessed by a raised hammer?
Q 33.
Define average power.
Q 34.
Is work a scalar quantity or a vector quantity ?
Q 35.
When a player hits a football it moves along the curved path and then falls to the ground. Calculate the work done by the force of gravity on the football.
Q 36.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 37.
Two bodies of masses m
1 and m
2 have equal kinetic energies. If p
1 and p
2 are their respective momentum, then ratio p
1 : p
2 is ___?
Q 38.
Fill in the blanks :
Work done by gravity on a falling body is available as ______ (kinetic/potential) energy on reaching the ground.
Q 39.
Identify the kind of energy possessed by a running athlete.
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.
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 42.
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 43.
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 44.
The kinetic energy of an object of mass,m moving with a velocity of 5 m/s is 25 J.What will be its kinetic energy when its velocity is doubled ? What will be its kinetic energy when its velocity increased three times ?
Q 45.
How is work done by a force measured ?
Q 46.
When is work done by a force positive ?
Q 47.
Name the device which converts electrical energy into mechanical energy.
Q 48.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 49.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 50.
What do you mean by the law of conservation of energy ?
