Question:
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 objjgft by the gravitational force ? Explain your answer.
Answer:
The work done by the gravitational force acting on the body of mass 10 kg (i.e., F = 10 kg wt) is zero when the body moves from A to B (s = AB) as shown in Fig.This is due to the reason that the force (F) and the displacement (5) are at right angles to each other.
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.
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 5.
What do the machines need for their working ?
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.
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 10.
When is work done by a force zero ?
Q 11.
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 12.
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 13.
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 14.
Fill in the blanks :
1 Joule = ____ × ____.
Q 15.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
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.
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 18.
Flowing water can rotate a turbine.What type of energy is used up by the turbine ?
Q 19.
How does the wind move the blades of a wind-mill ?
Q 20.
Is Work a scalar or vector quantity?
Q 21.
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 22.
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 23.
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Q 24.
What are the various energy transformations that occur when you are riding a bicycle ?
Q 25.
What are the units of work and energy ?
Q 26.
What do you understand by the term energy ? Give its scientific conception.
Q 27.
What do you mean by power of an agent ? Give an expression for power.
Q 28.
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 29.
How do you differentiate between energy and power ?
Q 30.
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 31.
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 32.
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Q 33.
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 34.
Fill in the blanks :
The sum of P.E. and K.E. is called __________.
Q 35.
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 36.
What is the relationship between kinetic energy and work?
Q 37.
Certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done by the force.
Q 38.
Can kinetic energy of an object be negative?
Q 39.
From where the falling raindrops gains kinetic energy?
Q 40.
Identify the kind of energy possessed by a running athlete.
Q 41.
What is the form of energy possessed by a running car?
Q 42.
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 43.
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 44.
A momentum of the body is increased by 20%. What is the percentage increase in its kinetic energy?
Q 45.
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 46.
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 47.
Define average power.
Q 48.
A battery lights a bulb.Describe the energy changes involved in the process
Q 49.
A certain household has consumed 250 units of energy during a month.How much energy is this in joules ?
Q 50.
When is work done by a force negative ?
