Question:
A roller coaster is shown in figure, at points i.e. ➊ and ➋, comparatively at what point (i) potential energy is maximum (ii) kinetic energy is maximum
Answer:
At point ➊, comparatively kinetic energy will be maximum and at point ➋ potential energy will be maximum.
Work and Energy
Q 1.
Name a machine that transforms muscular energy into useful mechanical work.
Q 2.
A body is thrown vertically upwards. Its velocity goes on decreasing. Write the change in kinetic energy when its velocity becomes zero.
Q 3.
What do the machines need for their working ?
Q 4.
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 5.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 6.
How does the wind move the blades of a wind-mill ?
Q 7.
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 8.
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 9.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 10.
When is work done by a force zero ?
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 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 13.
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 14.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 15.
A freely falling object eventually stops on reaching the ground.What happens to its kinetic energy ?
Q 16.
What is the form of energy possessed by a running car?
Q 17.
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 18.
Can a body have energy without having momentum ?
Q 19.
Name two forms of mechanical energy.
Q 20.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 21.
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 22.
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 23.
Define average power.
Q 24.
Name the device which converts electrical energy into mechanical energy.
Q 25.
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 26.
Is a person doing any work by holding a suitcase ?
Q 27.
Is energy a vector quantity ?
Q 28.
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 29.
Fill in the blanks :
Work done against a force is stored as _____.
Q 30.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 31.
Fill in the blanks :
Work done against gravity in lifting a mass is stored as ______. Numerically, it is equal to m ×_ ×__.
Q 32.
From where the falling raindrops gains kinetic energy?
Q 33.
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 34.
Define 1 W of power.
Q 35.
Fill in the blanks :
A form of energy an object has because of its motion is called ________.
Q 36.
A heavy stone is lowered to the ground with the help of rope. Is the work done by the applied force positive or negative?
Q 37.
Name the type of energy possessed by a raised hammer?
Q 38.
Calculate potential energyof a person having 60 kg mass on the summit of Mt. Everest. Height of Mt. Everest is 8848 m from sea level. (g = 9.8 m/s
2)
Q 40.
The work done by the heart is I J per beat.Calculate the power of the heart if it beats 72 times/min.
Q 41.
When is work done by a force positive ?
Q 42.
Why do some engines require fuels like petrol and diesel ?
Q 43.
What is the work done by a constant force ?When is it positive,negative or zero ?
Q 44.
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 45.
Fill in the blanks :
Ability to do work is called _______.
Q 46.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 47.
A roller coaster is shown in figure, at points i.e. ➊ and ➋, comparatively at what point (i) potential energy is maximum (ii) kinetic energy is maximum
Q 48.
Assuming the earth revolves around the sun in a perfect circular orbit due to centripetal force exerted by the Sun. Is the work done by the Sun positive or negative.
Q 49.
What is a conservative forces? Give an example.
Q 50.
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.
