Question:
What do you understand by the term energy ? Give its scientific conception.
Answer:
Refer to Art. 5.4,Page 263.
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.
How do you differentiate between energy and power ?
Q 3.
Define kinetic energy.Give some examples of bodies possessing kinetic energy.
Q 4.
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 6.
Name the type of energy possessed by a raised hammer.
Q 7.
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 8.
Name a machine that transforms muscular energy into useful mechanical work.
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.
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 12.
What do you mean by the law of conservation of energy ?
Q 13.
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 14.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 15.
What do you mean by work ?Give its scientific conception.
Q 16.
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 17.
Define average power.
Q 18.
Calculate the power of an engine required to lift 105 kg of coal per hour from a mine 360 m deep.
Q 19.
A certain household has consumed 250 units of energy during a month.How much energy is this in joules ?
Q 20.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 21.
Can a body have energy without having momentum ?
Q 22.
When is work done by a force zero ?
Q 23.
What do the machines need for their working ?
Q 24.
What is the difference between potential energy and kinetic energy ?
Q 25.
What do you mean by kinetic energy ? Derive an expression for the kinetic energy of an object of mass m moving with velocity,v.
Q 26.
Is Work a scalar or vector quantity?
Q 27.
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 28.
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 29.
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 30.
An electric heater is rated 1500 W.How much energy does it use in 10 hours ?
Q 31.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 32.
How does the wind move the blades of a wind-mill ?
Q 33.
What is the form of energy possessed by a running car?
Q 34.
What is Kilowatt hour?
Q 35.
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 36.
A man exerts a force of 200 N in pulling a cart at a constant speed of 16 m/s.Calculate the power spent by the man.
Q 37.
What do you understand by the term energy ? Give its scientific conception.
Q 39.
Fill in the blanks :
Work done against a force is stored as _____.
Q 40.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 41.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
Q 42.
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 43.
Write an expression for kinetic energy of an object
Q 44.
Is work a scalar quantity or a vector quantity ?
Q 45.
Give an example where potential energy is acquired by a body due to change of its shape.
Q 46.
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 47.
Fill in the blanks :
Work is a ______ (scalar/vector) quantity.
Q 48.
Fill in the blanks :
Work done is positive when the angle between force and displacement is ____ (acute/obtuse)
Q 49.
Fill in the blanks :
If the mass is doubled while its speed remains the same, the kinetic energy will be _____ (be same/double/four times) of the initial kinetic energy.
Q 50.
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
