Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 40

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Question 1
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According to the Newton's third law of motion, action and reaction pair:

A
always act on the same body

B
always act on different bodies in opposite directions

C
have same magnitude and directions

D
act on either body at normal to each other

Solution

For every action, there is an equal and opposite reaction.
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.
Question 2
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Which of the following requires a pushing force?

A
Throwing a stone at a bird.

B
Grabbing hold of a pencil.

C
Leaves falling from a tree.

D
A load lifted by a pulley.

Solution

When we throw a stone at a bird, we need to apply a push on the stone so that it moves. Options B, C, D needs a pulling force.
Question 3
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A force of $$5\ N$$ produces an acceleration of 8 $$ms^{-2}$$ on a mass $$m_1$$ and an acceleration of 24 $$m s^{-2}$$ on a mass $$m_{2}$$ . What acceleration (in $$ms^{-2}$$) would the same force provide if both the masses are tied together?

A
$$4$$

B
$$5$$

C
$$6$$

D
$$7$$

Solution

From Newton's second law of motion, the applied force is directly proportional to the acceleration produced or $$F = m a$$
The unit of force is newton in SI denoted by the symbol N.
Forces acting on a mass $$m_1$$ with acceleration $$a_1$$ and mass $$m_2$$ with acceleration $$a_2$$ are as given below.
$$m_{1}=\dfrac{F}{a_{1}}=\dfrac{5}{8}kg.$$
$$m_{2}=\dfrac{F}{a_{2}}=\dfrac{5}{24}kg.$$
$$M=\left ( \dfrac{5}{8}+\dfrac{5}{24} \right )kg=\left ( \dfrac{5}{6} \right )kg$$
Acceleration produced in M (when the two masses are tied together),
$$a=\dfrac{F}{M}=\dfrac{5}{\dfrac{5}{6}}=6 \ m s^{-2}$$
Question 4
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Suppose a ball of mass m is thrown vertically upward with an initial speed v. Its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of initial and final momentums of the ball are same. Is this an example of conservation of momentum?

A
Yes

B
No

C
Sometimes

D
None of these

Solution

Law of conservation of momentum is applicable to isolated system (no external force is applied).
In this case, the change in velocity is due to the gravitational force of earth.When the ball is thrown up, negative force of gravity is applied and so the speed becomes zero.After that due to gravitational force the ball falls down with same initial velocity.
Question 5
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While dusting a carpet, we give a sudden jerk or beat with a stick because :

A
Inertia of rest keeps the dust in its position and the dust is removed by movement of carpet away.

B
Inertia of motion removes dust.

C
No inertia involved in process.

D
None of the above

Solution

When carpet is given sudden jerk, due to inertia dust particles does not change position, while carpet moves.
Thus dust particles gets separated from carpet.
So, Option A is correct.
Question 6
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In a game of tug of wars, a condition of equilibrium exists. Both the teams pull the rope with a force of 10$$^4$$ N. The tension in the rope is :

A
10$$^4$$ N

B
10$$^5$$ N

C
0 N

D
2 $$\times $$ 10$$^4$$ N

Solution

In a game of tug of wars, a condition of equilibrium exists. Both the teams pull the rope with a force of 10$$^4$$ N. The tension in the rope is equal and opposite to the force with which both teams pull the rope i.e., 10$$^4$$ N.
Question 7
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During a planned manoeuvre in a space flight, a free-floating astronaut A pushes another free floating astronaut B, the mass of A being greater than that of B. Then, the magnitude of the force exerted by astronaut A on astronaut B is:

A
equal to zero

B
equal to the force exerted by B on A

C
greater than the force exerted by B on A

D
less than the force exerted by B on A

Solution

According to Newton third law every , every action and equal and opposite reaction, the moment A pushes B with force F , so A will also experience the same force F but in opposite direction.
Question 8
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What are action-reaction forces?

A
Those which act on the same body.

B
Those which act on different bodies in different directions

C
Those which act vertically.

D
Those which act in the same direction

Solution
Question 9
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The state of rest or state of motion of a body can be changed by using

A
Pressure

B
Force

C
Heat

D
None of these

Solution

First law of motion:
A body in rest or a body in motion will continue to do that unless and until an external force is applied on it.
Force will accelerate or decelerate a body.
Question 10
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If action and reaction were to act on the same body then

A
resultant would be zero

B
body would not move at all

C
both (a) and (b)

D
none of these

Solution

According to Newton's third law:
Every action has an equal and opposite reaction. As soon as we apply a force on a body, there is a resultant opposite force generated.

In other words the action and reaction forces occur in pair.Hence if action and reaction were to act on the same body then the resultant is zero and ultimately the body does not move.

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Re-Attempt Weekly Quiz Competition

Forces and Laws of Motion Test - 40

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Forces and Laws of Motion Test - 40

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Question 1

always act on the same body

always act on different bodies in opposite directions

have same magnitude and directions

act on either body at normal to each other

Solution

Question 2

Throwing a stone at a bird.

Grabbing hold of a pencil.

Leaves falling from a tree.

A load lifted by a pulley.

Solution

Question 3

$$4$$

$$5$$

$$6$$

$$7$$

Solution

Question 4

Yes

No

Sometimes

None of these

Solution

Question 5

Inertia of rest keeps the dust in its position and the dust is removed by movement of carpet away.

Inertia of motion removes dust.

No inertia involved in process.

None of the above

Solution

Question 6

10$$^4$$ N

10$$^5$$ N

0 N

2 $$\times $$ 10$$^4$$ N

Solution

Question 7

equal to zero

equal to the force exerted by B on A

greater than the force exerted by B on A

less than the force exerted by B on A

Solution

Question 8

Those which act on the same body.

Those which act on different bodies in different directions

Those which act vertically.

Those which act in the same direction

Solution

Question 9

Pressure

Force

Heat

None of these

Solution

Question 10

resultant would be zero

body would not move at all

both (a) and (b)

none of these

Solution

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