Question:
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?
Answer:
(i) Sandy’s IKE ranks second among all the hurricanes so far-Hurricane Isabel in 2003 was more devastating.
(ii) Over 140 TJ (1 TJ = 1 trillion joule = 2,77,778 kWh) -it generated more energy than Hiroshima atomic bomb.
(iii) Katrina’s IKE was more concentrated whereas Sandy’s IKE was more spread out.
(iv)Universal sympathy and deep concern for those affected by Sandy’s outrage.
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.
What do the machines need for their working ?
Q 4.
How does the wind move the blades of a wind-mill ?
Q 5.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 6.
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 7.
Name a machine that transforms muscular energy into useful mechanical work.
Q 8.
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 9.
What is the form of energy possessed by a running car?
Q 10.
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 11.
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 12.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 13.
Name two forms of mechanical energy.
Q 14.
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 15.
Why do some engines require fuels like petrol and diesel ?
Q 16.
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 17.
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 18.
Is a person doing any work by holding a suitcase ?
Q 19.
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 20.
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 21.
What is the work done by a constant force ?When is it positive,negative or zero ?
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.
Fill in the blanks :
Ability to do work is called _______.
Q 24.
Name the device which converts electrical energy into mechanical energy.
Q 25.
Can a body have energy without having momentum ?
Q 26.
Is energy a vector quantity ?
Q 28.
Name the type of energy possessed by a raised hammer?
Q 29.
Write an expression for the kinetic energy of an object in terms (i) velocity (
v) of an object (ii) in terms of momentum (
p) of an object.
Q 30.
A body of mass 15 kg undergoes downward displacement of 40m under the effect of gravitational force. How much work is done? (take g = 10 m/s
2)
Q 31.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 32.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 33.
Define average power.
Q 34.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 35.
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 is increased three times?
Q 36.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 37.
Is work a scalar or vector quantity?
Q 38.
A battery lights a bulb. Describe the energy changes involved in the process.
Q 39.
Name the type of energy possessed by the following? (i) Stretched slinky (ii) Speeding car
Q 40.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 41.
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 42.
What is Kilowatt hour?
Q 43.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 44.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
Q 45.
Define 1 J of work.
Q 46.
Define 1 W of power.
Q 47.
A lamp consumes 1000 J of electrical energy is 10 s.What is its power ?
Q 48.
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 49.
When is work done by a force zero ?
Q 50.
Is work a scalar quantity or a vector quantity ?
