Question:
What do the machines need for their working ?
Answer:
Since machines are meant to convert energy into work,all machines need energy for their working.
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.
Name a machine that transforms muscular energy into useful mechanical work.
Q 3.
How do you differentiate between energy and power ?
Q 4.
What do you mean by work ?Give its scientific conception.
Q 5.
Define kinetic energy.Give some examples of bodies possessing kinetic energy.
Q 6.
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 7.
Name the type of energy possessed by a raised hammer.
Q 8.
What do the machines need for their working ?
Q 9.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 10.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 11.
Can a body have energy without having momentum ?
Q 12.
Write an expression for kinetic energy of an object
Q 13.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 14.
What is the difference between potential energy and kinetic energy ?
Q 15.
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 16.
Define average power.
Q 17.
Define 1 J of work.
Q 18.
Fill in the blanks :
A force acting on a body shows a displacement in the direction of the force. It is said _______ is done on the body.
Q 19.
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 20.
An electric bulb of 60 W is used for 6 h per day.Calculate the ‘units’ of energy consumed in one day by the bulb
Q 21.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 22.
What do you mean by the law of conservation of energy ?
Q 23.
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 24.
The magnitude of momentum of a moving object is equal to its kinetic energy. What will be the velocity of the object considering SI units for the system?
Q 25.
What are other forms of energies apart from mechanical energy? Does Law of Conservation of Energy apply to all of them?
Q 26.
What are the various energy transformations that occur when you are riding a bicycle?
Q 27.
Two bodies of equal masses move with uniform velocities v and 3 v respectively.Find the ratio of their kinetic energies.
Q 28.
When is work done by a force zero ?
Q 29.
Is work a scalar quantity or a vector quantity ?
Q 30.
How does the wind move the blades of a wind-mill ?
Q 31.
What do you understand by the term energy ? Give its scientific conception.
Q 32.
What do you mean by power of an agent ? Give an expression for power.
Q 33.
Is it possible to havfc a situation where mechanical energy (E) - potential energy (
) Is negative,i.e.,(E-
)< 0.
Q 34.
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 35.
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 36.
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 37.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 38.
If the momentum of a body is increased
n times, its kinetic energy increases (a) n times (b) 2n times (c) √n times (d) n
2 times
Q 39.
What is a horsepower?
Q 40.
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 41.
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 42.
Calculate the power of an engine required to lift 105 kg of coal per hour from a mine 360 m deep.
Q 43.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 44.
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 45.
Define 1 J of work.
Q 46.
Is Work a scalar or vector quantity?
Q 47.
Fill in the blanks :
Work done against a force is stored as _____.
Q 48.
A boy of mass 45 kg climbs up 20 steps in 20 second. If each step is 25 cm high, calculate the power used in climbing
Q 49.
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 50.
Is it possible that a force acts on a body still the work done is zero? Explain with an example.
