Laws of Motion Test

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Laws of Motion Test - 18

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Question 1
1 / -0

The impulse of a body is equal to :

A
Rate of change of its momentum.

B
Change in its momentum.

C
The product of force applied on it and the time of application of the force.

D
Both (B) and (C)

Solution

impulse of a body is change in momentum if over a countable time .and rate of change in momentum if taken over very small time period.
so the answer is D.
Question 2
1 / -0

A car and a lorry are moving with same momentum, if same braking force is applied, then :

A
Car comes to rest in shorter distance.

B
Lorry comes to rest in shorter distance.

C
Both travels same distance before coming to rest.

D
None

Solution

A car and a lorry are moving with same momentum, if same breaking force is applied, then lorry comes to rest in shorter distance as it has greater mass so moves with less velocity.
Question 3
1 / -0

The average force necessary to stop a hammer with 25 N-s momentum in 0.05s expressed in N is :

A
500

B
125

C
50

D
250

Solution

Impulse $$=$$ Force $$\times$$ time
$$25 = F \times 0.05$$
$$F = \displaystyle \frac{25}{0.05} = 500 N$$
Question 4
1 / -0

If two balls each of mass 0.6 kg moving in opposite directions with speed of 4 m s$$^{-1}$$ collide and rebound with same speed, then the impulse imparted to each ball due to other is:

A
$$0.48 kg m s^{-1}$$

B
$$0.53 kg m s^{-1}$$

C
$$0.81 kg m s^{-1}$$

D
$$0.92 kg m s^{-1}$$

Solution

Impulse
$$= F \times t=$$ change in momentum
$$=$$ 0.06 (4-(-4))
$$=$$ 0.48 kg m s$$^{-1}$$
Question 5
1 / -0

A force acts on a body of mass 3 kg such that its velocity changes from 4 m s$$^{-1}$$ to 10 m s$$^{-1}$$. The change in momentum of the body is :

A
42 kg m s$$^{-1}$$

B
2 kg m s$$^{-1}$$

C
18 kg m s$$^{-1}$$

D
11 kg m s$$^{-1}$$

Solution

$$\Delta p = m(v-u) = 3 (10-4)$$
$$=18 kg m s^{-1}$$
Question 6
1 / -0

The time, in which a force of 2 N produces a change as momentum of 0.4 kg m s$$^{-1}$$ in the body is :

A
0.2s

B
0.02s

C
0.5s

D
0.05s

Solution

$$F=\displaystyle \frac{\Delta P}{t}$$
$$2 = \displaystyle \frac{0.4}{t} $$ (or) $$t = 0.2 s$$
Question 7
1 / -0

A hammer of mass 5 kg moving with a speed of 2 m s$$^{-1}$$ strikes the head of a nail driving it 20 cm into the wall. Find the impulse.

A
10 N s

B
20 N s

C
30 N s

D
40 N s

Solution

Impulse $$=$$ m(v - u)
$$=$$ 5 (0 - 2)
$$=$$ 10 N s
Question 8
1 / -0

A man getting down from a running bus falls forward :

A
as the forward movement of bus tries to pull the man forward

B
due to inertia the upper part of the body moves in the forward direction while feet come to the rest as soon as they touch the road

C
as he leans forward as a matter of habit

D
due to the combination effect of all the three factors stated in $$(A),(B)$$ and $$(C)$$
Solution
Hint: Due to inertia, the body in motion stays in motion and the body in rest remains stationary unless it is affected by an external force.

Explanation:
- According to Newton’s first law of motion, the body in motion stays in motion unless it is affected by an external force.
- The inertia of a body is the tendency of the body to remain in motion, even when the applied force on the body is removed.
- The person in the bus moves in the same direction of the motion of the bus. When the person steps out of the bus, his feet do not move but his upper body moves in the direction of the bus due to inertia of motion.
Hence, a man getting down from a running bus falls forward due to inertia the upper part of the body moves in the forward direction while feet come to the rest as soon as they touch the road.
Correct Option: B
Question 9
1 / -0

How does the proper inflation of tyre save fuel?

A
Normal reaction decreases.

B
Normal reaction increases.

C
Sliding contact with the road decreases.

D
Sliding contact with the road increases.

Solution

When the tyre is properly inflated, its contact area with the road decreases which reduces the sliding contact. However, as the friction does not depend on area so the frictional force and thus the normal reaction remains unchanged.

Hence, correct answer is option $$C$$
Question 10
1 / -0

....................... is a self adjusting force.

A
Magnetic Force

B
Electrostatic Force

C
Frictional Force

D
All

Solution

$$\textbf{Part1: Definition}$$
$$\bullet$$ Self-adjusting force is defined as a force which can adjust itself as required by the situation. It can increase or decrease itself with the change made in the system.
$$\textbf{Part2: }$$
$$\bullet$$ If the surface of two bodies are in contact with each other and we apply a force on one of them, static friction will appear, even if the body is at rest.
$$\bullet$$ The static friction will try to make the body to remain at rest. If we apply an external force on the body the static friction will adjust the magnitude of friction force and try to make the object to remain at rest.
$$\bullet$$ It has a limit between $$0$$ and $$\mu N$$ where N is the normal reaction and $$\mu$$ is coefficient of friction . It opposes the externally applied force between these limits.
So, we can say that static friction is a self-adjusting force because it does not have any fixed magnitude, but it will adjust the force according to the applied force.
Hence , option (c) is correct.

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Laws of Motion Test - 18

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Laws of Motion Test - 18

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Question 1

Rate of change of its momentum.

Change in its momentum.

The product of force applied on it and the time of application of the force.

Both (B) and (C)

Solution

Question 2

Car comes to rest in shorter distance.

Lorry comes to rest in shorter distance.

Both travels same distance before coming to rest.

None

Solution

Question 3

500

125

50

250

Solution

Question 4

$$0.48 kg m s^{-1}$$

$$0.53 kg m s^{-1}$$

$$0.81 kg m s^{-1}$$

$$0.92 kg m s^{-1}$$

Solution

Question 5

42 kg m s$$^{-1}$$

2 kg m s$$^{-1}$$

18 kg m s$$^{-1}$$

11 kg m s$$^{-1}$$

Solution

Question 6

0.2s

0.02s

0.5s

0.05s

Solution

Question 7

10 N s

20 N s

30 N s

40 N s

Solution

Question 8

as the forward movement of bus tries to pull the man forward

due to inertia the upper part of the body moves in the forward direction while feet come to the rest as soon as they touch the road

as he leans forward as a matter of habit

due to the combination effect of all the three factors stated in $$(A),(B)$$ and $$(C)$$

Solution

Question 9

Normal reaction decreases.

Normal reaction increases.

Sliding contact with the road decreases.

Sliding contact with the road increases.

Solution

Question 10

Magnetic Force

Electrostatic Force

Frictional Force

All

Solution

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