Work and Energy - Maharashtra Board STD 9 Science Questions

Q 1MCQ1 Mark

The device which converts mechanical energy into energy which runs our microwave oven is:

A
Electric motor.
✓
Alternator.
C
Turbine.
D
Electric heater.

Answer: B.

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Q 2MCQ1 Mark

The work done on an object does not depend on the:

A
Displacement.
B
Angle between force and displacement.
C
Force applied.
✓
Initial velocity of the object.

Answer: D.

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Q 3MCQ1 Mark

In case of negative work, the angle between the force and displacement is:

A
$0^\circ$
B
$45^\circ$
C
$90^\circ$
✓
$180^\circ$

Answer: D.

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Q 4MCQ1 Mark

A girl is carrying a school bag of $3\ kg$ mass on her back and moves $200\ m$ on a levelled road. If the value of g be $10\ m/s^2$, the work done by the girl against the gravitational force will be:

A
$6000\ J$
B
$0.6\ J$
✓
$0\ J$
D
$6\ J$

Answer: C.

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Q 5MCQ1 Mark

A car is accelerated on a levelled road and acquires a velocity $4$ times of its initial velocity. During this process, the potential energy of the car:

✓
Does not change.
B
Becomes twice that of initial potential energy.
C
Becomes 4 times that of initial potential energy.
D
Becomes 16 times that of initial potential energy.

Answer: A.

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Q 6Question Answer (2 Marks)2 Marks

A trolley is pushed along a road with a force of 400N through a distance of 60m in 1 minute. Calculate the power developed.

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Q 7Question Answer (2 Marks)2 Marks

Two bodies having equal masses are moving with uniform speeds of $v$ and $2v$ respectively. Find the ratio of their kinetic energies.

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Q 8Question Answer (2 Marks)2 Marks

In an experiment to measure his power, a student records the time taken by him in running in a flight of steps on a staircase. Use the following data to calculate the power of the student:
Number of steps $= 28$
Height of each step $= 20\ cm$
Time taken $= 5.4\ s$
Mass of student $= 55\ kg$
Acceleration $= 9.8ms^{-2}$
Due to gravity.

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Q 9Question Answer (2 Marks)2 Marks

A man is instructed to carry a package from the base camp at B to submit A of a hill at a height of $1200$ metres. The man weighs $800\ N$ and the package weighs $200\ N$. If $g = 10m/s^2$,

How much work does man do against gravity?
What is the potential energy of the package at A if it is assumed to be

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Q 10Question Answer (2 Marks)2 Marks

The work done by a force acting obliquely is given by the formula: $\text{W} =\text{F}\cos\theta\times\text{s}.$ What will happen to the work done if angle between the direction of force and motion of the body is increased gradually? Will it increase, decrease or remain constant?

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Q 11Question Answer (1 Marks)1 Mark

Name five appliances or machines which use an electric motor.

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Q 12Question Answer (1 Marks)1 Mark

What is the power of a body which is doing work at the rate of one joule per second?

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Q 13Question Answer (1 Marks)1 Mark

Name the device or machines which convert:
Electrical energy into sound energy.

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Q 14Question Answer (1 Marks)1 Mark

Name the device or machines which convert:
Chemical energy into electrical energy.

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Q 15Question Answer (1 Marks)1 Mark

Name the device or machines which convert:
Light energy into heat energy.

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Q 16Question Answer (3 Marks)3 Marks

A body of mass $2\ kg$ is thrown vertically upwards with an initial velocity of $20\ m / s$. What will be its potential energy at the end of $2\ s$ ? (Assume $g =10 m / s ^2$ ).

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Q 17Question Answer (3 Marks)3 Marks

A man drops a $10\ kg $rock from the top of a $5\ m$ ladder. What is its speed just before it hits the ground? What is its kinetic energy when it reaches the ground? $\left(8=10 m / s ^2\right)$

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Q 18Question Answer (3 Marks)3 Marks

Explain how, the total energy a swinging pendulum at any instant of time remains conserved. Illustrate your answer with the help of a labeled diagram.

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Q 19Question Answer (3 Marks)3 Marks

A man weighing 500N carried a load of 100N up a fighter of stairs 4m high in 5 seconds. What is the power?

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Q 20Question Answer (3 Marks)3 Marks

A weightlifter is lifting weights of mass $200\ kg$ up to a height of $2$ metres. If $g = 9.8\ ms^{-2}$, Calculate:

Potential energy acquired by the weights.
Work done by the weightlifter.

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Q 21Question Answer (5 Marks)5 Marks

A body of $2\ kg$ falls from rest. What will be its kinetic energy during the fall at the end of $2 s$ ? (Assume $g =10\ m / s ^2$ )

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Q 22Question Answer (5 Marks)5 Marks

State and explain the law of conservation of energy with an example.

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Q 23Question Answer (5 Marks)5 Marks

A ball of mass $200\ g$ falls from a height of $5$ metres. What is its kinetic energy when it just reaches the ground? $(8=$ $9.8 m / s$ ).

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Q 24Question Answer (5 Marks)5 Marks

Two objects having equal masses are moving with uniform velocities of 2m/s and 6m/s respectively. Calculate the ratio of their kinetic energies.

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Q 25Question Answer (5 Marks)5 Marks

A bullet of mass $15\ g$ has a speed of $400\ m/s$. What is its kinetic energy? If the bullet strikes a thick target and is brought to rest in $2\ cm$, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet?

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