Question:
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.
Answer:
Yes.In the absence of any force on the object, i.e.,F = 0, ma = 0(as F= ma).Since m ≠0,a = 0.In such a case,the object is either at rest or in a state of uniform motion in a straight line.In the latter case,there is a displacement of the object without any force acting on it.
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 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 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.
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.
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 20.
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 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.
Can a body have energy without having momentum ?
Q 25.
Is energy a vector quantity ?
Q 26.
Name the device which converts electrical energy into mechanical energy.
Q 28.
Name the type of energy possessed by a raised hammer?
Q 29.
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 30.
Define average power.
Q 31.
A battery lights a bulb. Describe the energy changes involved in the process.
Q 32.
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 33.
How much work is done on a body of mass 1kg whirling on a circular path of radius 5m?
Q 34.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 35.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Q 36.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 37.
When is work done by a force zero ?
Q 38.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 39.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 40.
What do you mean by power of an agent ? Give an expression for power.
Q 41.
In physics,energy is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems.However,this must be understood as an overly simplified definition as we shall come to know in higher classes that not all energy can perform work.
(a) How did the concept of energy emerge ?
(b) How much electric energy is generated in a typical lightning strike ? What are the forms to which this energy gets converted ?
(c) What is the kinetic energy of a passenger seated in a moving plane :(i) with respect to the plane (ii) with respect to the Earth.
Q 42.
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 43.
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 44.
Fill in the blanks :
Ability of a body to do work due to its position or configuration is known as _________ of the body.
Q 45.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 46.
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 47.
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 48.
Fill in the blanks :
SI Unit of work is _______.
Q 49.
Fill in the blanks :
1 Joule = ____ × ____.
Q 50.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
