Work Energy and Power Test

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Work Energy and Power Test - 16

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Weekly Quiz Competition

Question 1
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What is potential energy?

A
Energy of an object due to its position or arrangement in a system

B
Energy of an object due to its nature or arrangement in a system

C
Energy of an object due to its shape or arrangement in a system

D
None

Solution

The potential energy is the stored energy of an object due to its position.
some examples of potential energies are gravitational potential energy, Electrostatic potential energy and elastic energy etc.
A body placed at ground will have less gravitational potential energy than a body placed at some height. therefore, potential energy changes by changing the position of object. Hence, Option A is correct.
Question 2
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A physics student is performing a experiment in which she twirls rubber stopper at the end of a string around in a circle at nearly constant speed and tries to determine its acceleration. Which of the following single changes would enables her to most nearly double the acceleration of the rubber stopper?

A
Double the speed of the rubber stopper.

B
Use a string that is twice as long as the original string.

C
Reduce the speed of the rubber stopper to half its original value.

D
Use a string that is half as long as the original string

E
Use a rubber stopper with twice as much mass as the original rubber stopper.

Solution

Due to constant speed , student is doing uniform circular motion so tangential acceleration is zero .
as the tangential acceleration is zero , therefore total acceleration will be equal to centripetal acceleration , which is
$$a=v^{2}/r$$
which can be doubled by using a string that is half as long as the original string .
$$a'=\dfrac{v^{2}}{\frac{r}{2}}=2a$$
Question 3
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A ride in an amusement park called scream machine swings the riders around a complete vertical circle during the course of the ride.
Identify where on ride rider feels the maximum speed?

A
Point A

B
Point B

C
Point C

D
Point D

E
Point E

Solution

At the lowermost position of the circular motion, the potential energy is zero and thus the kinetic energy of the rider is maximum at that position.
Using $$K.E = \dfrac{1}{2}mv^2 $$
Hence the rider feels maximum speed at the lowermost position of motion i.e point A.
Question 4
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A ball of mass $$m$$ is attached with the string of length $$R$$, rotating in a circular motion, with instantaneous velocity $$v$$ and centripetal acceleration $$a$$.
Calculate the centripetal acceleration of the ball if its mass is doubled?

A
$${a}/{4}$$

B
$${a}/{2}$$

C
$$a$$

D
$$2a$$

E
$$4a$$

Solution

As centripetal acceleration is given by $$a=v^{2}/R$$
therefore centripetal acceleration does not depend upon mass of ball, so it will remain constant ,equal to $$a$$.
Question 5
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Identify the correct statement of Work-Energy Theorem :

A
Work done by all the forces on a particle to displace it is equal to its change in kinetic energy.

B
Work done by all the forces on a particle is equal to its change in mechanical energy .

C
Work done by all the forces acting on a particle is equal to change in its potential energy.

D
Work done by a force on a particle is equal to change in its kinetic energy.

Solution

The work-energy theorem states that the work done by all forces acting on a particle equals the change in its kinetic energy.

Hence correct answer is option $$A$$
Question 6
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A simple pendulum, composed of a bob of mass $$m$$ connected to the end of a massless rod, executes simple harmonic motion as it swings through small angles of oscillation.The maximum angular displacement with the vertical is denoted by $${ \theta }_{ max }$$. Frictional effects and variation of acceleration due to gravity are negligible.
Which one of the following would enable you to calculate the length of the pendulum?

A
The mass of the bob

B
The period of the oscillations

C
The tangential acceleration at $$\theta = 0$$

D
The maximum speed of the bob

E
The acceleration at $$\theta = {\theta}_{max}$$

Solution

For the small oscillation, the motion of the pendulum can be treat as a simple harmonic motion. So, time period of a SHM is $$T=2\pi\sqrt{\frac{l}{g}}$$
Thus, time period would enable you to calculate the length of the pendulum.
Question 7
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A ball with mass m and speed $$V_0$$ hit a wall and rebounds back with same speed.
Calculate the change in the object's kinetic energy.

A
$$-mv_0 ^2$$

B
$$- \frac{1}{2}mv_0 ^2$$

C
Zero

D
$$ \frac{1}{2}mv_0 ^2$$

E
$$mv_0 ^2$$

Solution

The speed of the ball remains the same $$v_0$$ before and after the collision with wall.
Thus the kinetic energy remains $$\dfrac{1}{2}mv_0^2$$.
Since kinetic energy is a scalar quantity, the change in it is zero.
Question 8
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A car and a lorry both are moving with equal kinetic energies. If equal braking force is applied on both, then before corning to rest:

A
The car will cover a greater distance

B
Lorry will cover a greater distance

C
Both will cover the same distance

D
The distance covered by them will depend only on their respective velocities.

Solution

The two moving objects have the same kinetic energy and the brakes equal retarding forces - so they will stop at the same time.
Hence, option C is correct.
Question 9
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What is kinetic energy?

A
Energy possessed by a body by the virtue of its motion

B
Energy possessed by a body by the virtue of its shape

C
Energy possessed by a body by the virtue of its size

D
None

Solution

Correct Option: A
Explanation: The energy which a body possesses by virtue of being in motion is called as kinetic energy. If we want to stop a moving body then we must do some work on the body to stop it which means that a moving body possesses energy because of motion.
If an object of mass $$m$$ moving with the velocity $$v$$, The kinetic energy is defined as,
$$K.E. = \dfrac{1}{2}mv^2$$
Hence, Option A is correct.
Question 10
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Which of the following will lead to a change in kinetic energy of a body?

A
change in its mass

B
change in its velocity

C
all of the above

D
none of the above

Solution

Kinetic energy of the body $$K = \dfrac{1}{2}mv^2$$
$$\implies$$ $$K \propto m$$ and $$K \propto v^2$$
Thus changing either the mass of the body or its velocity will lead to a change in kinetic energy of a body.

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Re-Attempt Weekly Quiz Competition

Work Energy and Power Test - 16

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Work Energy and Power Test - 16

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SHARING IS CARING

Question 1

Energy of an object due to its position or arrangement in a system

Energy of an object due to its nature or arrangement in a system

Energy of an object due to its shape or arrangement in a system

None

Solution

Question 2

Double the speed of the rubber stopper.

Use a string that is twice as long as the original string.

Reduce the speed of the rubber stopper to half its original value.

Use a string that is half as long as the original string

Use a rubber stopper with twice as much mass as the original rubber stopper.

Solution

Question 3

Point A

Point B

Point C

Point D

Point E

Solution

Question 4

$${a}/{4}$$

$${a}/{2}$$

$$a$$

$$2a$$

$$4a$$

Solution

Question 5

Work done by all the forces on a particle to displace it is equal to its change in kinetic energy.

Work done by all the forces on a particle is equal to its change in mechanical energy .

Work done by all the forces acting on a particle is equal to change in its potential energy.

Work done by a force on a particle is equal to change in its kinetic energy.

Solution

Question 6

The mass of the bob

The period of the oscillations

The tangential acceleration at $$\theta = 0$$

The maximum speed of the bob

The acceleration at $$\theta = {\theta}_{max}$$

Solution

Question 7

$$-mv_0 ^2$$

$$- \frac{1}{2}mv_0 ^2$$

Zero

$$ \frac{1}{2}mv_0 ^2$$

$$mv_0 ^2$$

Solution

Question 8

The car will cover a greater distance

Lorry will cover a greater distance

Both will cover the same distance

The distance covered by them will depend only on their respective velocities.

Solution

Question 9

Energy possessed by a body by the virtue of its motion

Energy possessed by a body by the virtue of its shape

Energy possessed by a body by the virtue of its size

None

Solution

Question 10

change in its mass

change in its velocity

all of the above

none of the above

Solution

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