Question:
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Answer:
Zero ∵ KE = ½ mv2 and v = 0
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
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 3.
What do the machines need for their working ?
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.
When is work done by a force zero ?
Q 8.
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 9.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 10.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 11.
What is the work done by a constant force ?When is it positive,negative or zero ?
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.
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 15.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 16.
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 17.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 18.
A battery lights a bulb.Describe the energy changes involved in the process
Q 19.
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 20.
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 21.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 22.
Name the type of energy possessed by a raised hammer?
Q 23.
A force of 5 N is acting on an object.The object is displaced through 2 m in the direction of the force.[in Fig.].If the force acts all through the displacement,find the work done by the force.
Q 24.
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 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 26.
Define average power.
Q 27.
Name two forms of mechanical energy.
Q 28.
Name a few forms of energy and their transformation into each other.
Q 29.
Many people debate about whether there is a God,or what God is.Is God an individual personality,sitting up in heaven listening to and granting our requests,or is God simply all the energy that exists in the Universe,or is God simply nature or the laws of nature ?
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.
Identify the kind of energy possessed by a running athlete.
Q 32.
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Q 33.
What is the kinetic energy of an object ?
Q 34.
Define 1 W of power.
Q 35.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 36.
When is work done by a force negative ?
Q 37.
Is work a scalar quantity or a vector quantity ?
Q 38.
What are the units of work and energy ?
Q 39.
Is energy a vector quantity ?
Q 40.
How is energy stored in a clock ?
Q 41.
Why do some engines require fuels like petrol and diesel ?
Q 42.
What is meant by the term potential energy ? Give its two examples.
Q 43.
Can a body have energy without having momentum ?
Q 44.
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?
Q 45.
When do we say that work is done?
Q 47.
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 48.
A force of 10 N moves a body with a constant speed of 2 m/s. Calculate the power of the body.
Q 49.
Is it possible that a force acts on a body still the work done is zero? Explain with an example.
Q 50.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
