Question:
What is mechanical energy? What are its types?
Answer:
Energy can exist in many forms like chemical energy, electrical energy, mechanical energy etc. Mechanical energy means the ability of to do work due to its position, configuration or motion. Thus mechanical energy is the sum of potential energy (PE) and kinetic energy (KE).
Work and Energy
Q 1.
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 2.
Name a machine that transforms muscular energy into useful mechanical work.
Q 3.
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 4.
What do the machines need for their working ?
Q 5.
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 6.
Fill in the blanks :
Work done is negative when the angle between force and displacement is ____ (acute/obtuse)
Q 8.
A 60 kg person climbs stairs of total height 20 m in 2 min.Calculate the power delivered.
Q 9.
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 10.
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 11.
When is work done by a force zero ?
Q 12.
Fill in the blanks :
1 Joule = ____ × ____.
Q 13.
Can kinetic energy of an object be negative?
Q 14.
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 15.
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 16.
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 17.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 18.
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 19.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Q 20.
Identify the kind of energy possessed by a running athlete.
Q 21.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 22.
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 23.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 24.
Is work a scalar quantity or a vector quantity ?
Q 25.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 26.
How does the wind move the blades of a wind-mill ?
Q 27.
What do you understand by the term energy ? Give its scientific conception.
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.
Is Work a scalar or vector quantity?
Q 30.
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 31.
Fill in the blanks :
A force acting on a body shows a displacement in the direction normal to the direction of the force. It is said _______ done on the body.
Q 32.
What is the relationship between kinetic energy and work?
Q 33.
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 34.
From where the falling raindrops gains kinetic energy?
Q 35.
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 36.
Give examples for the following scenarios of energy transformations. You may choose the answer(s) from the following list of words
solar cell, turbine, mixer, fan, steam engine, automobiles, green plants, nuclear reactor, electric bulb, torch, electric bulb, microphone, loudspeaker, geyser, heater, car battery, inverter, LPG
| SNo. |
Energy Transformation
From ⟶ To |
Give Example |
| 1. |
Mechanical ⟶ Electrical |
_________ |
| 2. |
Electrical ⟶ Mechanical |
_________ |
| 3. |
Electrical ⟶ Heat |
_________ |
| 4. |
Heat ⟶ Mechanical |
_________ |
| 5. |
Electrical ⟶ Light |
_________ |
| 6. |
Electrical ⟶ Sound |
_________
|
| 7. |
Chemical ⟶ Heat |
_________ |
| 8. |
Electrical ⟶ Chemical |
_________ |
| 9. |
Sound ⟶ Electrical |
_________ |
| 10. |
Chemical ⟶ Electrical |
_________ |
| 11. |
Light ⟶ Electric |
_________ |
| 12. |
Chemical ⟶ Mechanical |
_________ |
| 13. |
Nuclear ⟶ Electrical |
_________ |
| 14. |
Light ⟶ Chemical |
_________ |
Q 37.
State the relation between commercial unit of energy and joules.
Q 38.
A body of mass 120 g is taken vertically upwards to reach the height of 5m. Calculate work done. (Take g = 10 m/s
2)
Q 39.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 40.
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 41.
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 42.
What is the kinetic energy of an object ?
Q 43.
Define average power.
Q 44.
A battery lights a bulb.Describe the energy changes involved in the process
Q 45.
When is work done by a force negative ?
Q 46.
What are the units of work and energy ?
Q 47.
What type of energy is possessed by a cricket ball just before being caught by a fielder ?
Q 48.
When an arrow is shot from a bow,it has kinetic energy.From where does it get the kinetic energy ?
Q 49.
What do you mean by the term potential energy ? Give some examples of bodies possessing potential energy ?
Q 50.
What do you mean by power of an agent ? Give an expression for power.
