Work and Energy Test

Result

Work and Energy Test - 48

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Question 1
1 / -0

Work is always done on a body when

A
a force acts on body to displace it.

B
it moves through a certain distance.

C
it experiences an increase in energy through a mechanical influence.

D
there is no displacement.

Solution

Work done is given by
$$W=Fd$$ where $$F$$ is Force and $$d$$ is displacement
Hence two conditions need to be satisfied for work to be done:
(i) a force should act on an object
(ii) the object must be displaced.
So option A is correct.
Question 2
1 / -0

The $$SI$$ unit of energy, the Joule is equivalent to

A
$$N-m$$

B
$$W/s$$

C
$$N-m^{2}/s^{2}$$

D
$$N/m$$

Solution
Question 3
1 / -0

The amount of work done on an object when a constant force of $$\dfrac { 1 }{ 10 }\ N$$ displaces it by $$10\ cm$$ along the line of action of the force is:

A
$$\dfrac { 1 }{ 10 }\ J$$

B
$$\dfrac { 1 }{ 100 }\ J$$

C
$$1\ J$$

D
$$10\ J$$

Solution

Given,
Force applied, $$F= \dfrac {1}{10}\ N$$

Displacement, $$d=10\ cm$$

$$d=\dfrac {10}{100}=\dfrac{1}{10} \ m$$

Work done, $$W=F\times d$$

$$W=\dfrac {1}{10} \times \dfrac{1}{10}$$

$$W=\dfrac {1}{100}\ J$$
Question 4
1 / -0

A lawn roller is pulled along a horizontal surface through a distance of $$20 \ m$$ by a rope with a force of $$200 \ N$$. If the rope makes an angle of $$60^o$$ with the vertical while pulling, the amount of work done by the pulling force is:

A
$$3464 \mathrm { J }$$

B
$$1000 \mathrm { J }$$

C
$$2000 \sqrt { 3 } \mathrm { J }$$

D
$$2000 \mathrm { J }$$
Solution
Correct Answer: Option A

Hint: Use the equation for work done, $$ W=Fscos\theta$$, where F is force, s is displacement and $$\theta$$ is the angle between force and displacement.

Explanation of Correct Option:
Given, force $$F=200N$$, distance $$s=20m$$,
Angle rope make with vertical is $$\theta=60^{\circ}$$, so angle rope makes with horizontal $$\theta=30^{\circ}$$
Work done by pulling force,$$W=F.s$$
$$W=Fscos\theta$$
$$W = 200 \times 20 \times \dfrac{\sqrt3}{2}$$ $$\left( {\because \theta = 30^\circ ,\cos 30^\circ = \dfrac{\sqrt3}{2}} \right)$$

$$W = 3464J$$

The amount of work done by pulling force is $$3464J$$ .
Question 5
1 / -0

In $$10 s$$, a body of $$6 kg$$ mass is dragged $$8 m$$ with uniform velocity across a floor by a steady force of $$20 N$$. The K.E of the body is:

A
$$2.92 J$$

B
$$0.92 J$$

C
$$1.92 J$$

D
$$0J$$

Solution
Question 6
1 / -0

A body of mass m is rotating in a vertical circle of radius 'r' with critical speed. The difference in its K.E. at the top and the bottom is _____.

A
2mgr

B
4 mgr

C
6 mgr

D
3 mgr

Solution
Question 7
1 / -0

A body of mass 0.5 kg is moving at a constant velocity, work done is

A
0 J

B
1.0 J

C
2.0 J

D
4.0 J

Solution

$$Work=Force \times displacement$$
Since moving with same velocity so no acceleration hence no force . So
$$W= 0\times displacement$$
$$W=0$$
Question 8
1 / -0

In which of the following, law of conservation of energy is violated?

A
Fusion of nuclei

B
Mud thrown on a wall

C
A satellite moving in elliptical orbit

D
None of these

Solution

The law of conservation of energy is never violated. in all the given processes, one form of energy is converted into other forms. But the total energy of the system is always conserved.
Question 9
1 / -0

Which of the following does not possess the ability to do work because of motion?

A
A sparrow flying in the sky

B
A sparrow moving slowly on the ground

C
A sparrow in the nest on a tree

D
A squirrel going up a tree

Solution
Question 10
1 / -0

If the kinetic Energy possessed by a man of $$50$$kg is $$625J$$, the speed of man is

A
$$5m{s^{ - 1}}$$

B
$$50m{s^{ - 1}}$$

C
$$0.5m{s^{ - 1}}$$

D
$$500m{s^{ - 1}}$$

Solution