Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 26

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Question 1
1 / -0

The force needed to produce an acceleration of $$6 m/s^2$$ in a ball of mass $$ 4 kg$$ will be

A
$$24 N$$

B
$$30 N$$

C
$$32 N$$

D
$$36 N$$

Solution

$$F=ma$$
$$F=6\times4$$
$$F=24N$$
So, the required force is $$F=24N$$.
Question 2
1 / -0

When will a body under the action of several forces have 0 acceleration?

A
When the vector sum of all the forces acting on the body is zero

B
When a body is very heavy

C
When the body is very light

D
When the body is a point body

Solution

Referring formula $$\displaystyle F =ma$$
Thus acceleration will be zero, when resultant force is zero. In option (d), the point body is to be considered. A point body does not mean a body of zero mass. A point body or a particle is ideally a piece or quantity of matter having practically no linear dimensions but only a position. The measure of this quantity of matter is the mass of the particle. It is a usual convention to imagine bodies as point objects when we are only concerned about their mass and not about the distribution of mass. Thus earth can be considered as a point body when we describe its motion about sun.
Question 3
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Every action has reaction. These action-reaction are

A
Equal, opposite and acting on the same body

B
Equal, in the same direction and acting on same body

C
Equal, opposite and acting on different bodies

D
Equal, in same direction and acting on different bodies.

Solution

According to Newton third law
The forces of action and reaction are equal, opposite and act on different bodies.
The effect of action and reaction is always visible separately on both the interacting bodies in opposite directions. Therefore, the forces of action and reaction are equal, opposite and act on different bodies.
Question 4
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A body is said to be underbalanced forces when the resultant force acting on the body is

A
Unity

B
Zero

C
Infinite

D
None of these

Solution

If the net force acting on a body is zero, then the body is said to be in equilibrium, or a body is said to be underbalanced forces when the resultant force acting on the body is zero.
Question 5
1 / -0

A driver accelerates his car first at the rate of 1.8 m/s$$^2$$ and then at the rate of 1.2 m/s$$^2$$. The ratio of the forces exerted by the engines will be respectively equal to

A
2 : 3

B
1 : 2

C
2 : 1

D
3 : 2

Solution

We have to find $$\dfrac{{F}_{1}}{{F}_{2}}$$
$$F\propto a$$
$$\dfrac{{F}_{1}}{{F}_{2}}=\dfrac{{a}_{1}}{{a}_{2}}$$.
Which gives the ratio $$3:2$$.
Question 6
1 / -0

When a force of 1 newton acts on a mass of 1 kg that is able to move freely, the object moves with a/an

A
speed of $$\displaystyle 1{ ms }^{ -1 }$$

B
acceleration of $$\displaystyle 1{ ms }^{ -2 }$$

C
speed of $$\displaystyle 1{ kms }^{ -1 }$$

D
acceleration of $$\displaystyle 10{ ms }^{ -2 }$$

Solution

According to Newton's second law of motion
$$ F= ma$$
Here,
Force $$F= 1 \ N$$
Mass $$m=1 \ kg$$
So,
$$ 1 \ N = (1 \ kg)\ \times a$$
$$\Rightarrow a =1 \ m/s^2 $$

Option B is correct.
Question 7
1 / -0

A ball of mass $$0.2 kg$$ moves with a velocity of $$20 m/s$$ and it stops in $$0.1 s$$, then the force on the ball is

A
$$40 N$$

B
$$20 N$$

C
$$4 N$$

D
$$2 N$$

Solution

$$\displaystyle F=ma=m\left( \frac { \upsilon -u }{ t } \right) =\frac { -mu }{ t } $$
Substituting the values and neglecting the negative sign (because none of the options is negative)
$$\displaystyle F=\frac { 0.2\times 20 }{ 0.1 } =40$$N
Question 8
1 / -0

When a body is in translatory equilibrium

A
The body is definitely at rest

B
The body is definitely in the state of uniform motion

C
The body will be either at rest or in the state or uniform motion

D
None of these

Solution

When a body is in translatory equilibrium , the net force acting on a body is zero, and the body is said to be in translational equilibrium. In translatory equilibrium, the center of mass of the body remains either at rest or moves rectilinearly with constant velocity. Hence, the body is definitely in the state of uniform motion or in rest.
Question 9
1 / -0

A body is said to be under balanced forces when the resultant force acting on the body is

A
unity

B
zero

C
infinite

D
none of these

Solution

Forces are said to be balanced if resultant of the forces is zero i.e. $$F_R = 0$$
Acceleration of the body $$a = \dfrac{F_R}{m} = 0$$
Thus a body under balanced forces has zero acceleration.
Question 10
1 / -0

A cannon after firing recoils due to

A
Conservation of energy

B
Backward thrust of gases produced

C
Newton's first law of motion

D
Newton's third law of motion

Solution

Correct Option is D.
Explanation for the correct:
$$\bullet$$ Newton's Third Law of Motion states that to every Action there is equal and opposite Reaction. Thus firing of bullet from cannon is an Action and there is opposite Reaction on the cannon due to which it recoils. Option D is correct.
$$\bullet$$ Conservation of Energy states that Energy can neither be created nor destroyed. It can only change it forms.
$$\bullet$$ Backward thrust of gases is not a Law. It is also one of the consequences of Third Law of Motion.
$$\bullet$$ First Law of Motion states that if a body is at rest/motion it will continue to remain at rest/motion until any external force is applied.

Thus, Only Option D is correct.

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Forces and Laws of Motion Test - 26

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Forces and Laws of Motion Test - 26

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Question 1

$$24 N$$

$$30 N$$

$$32 N$$

$$36 N$$

Solution

Question 2

When the vector sum of all the forces acting on the body is zero

When a body is very heavy

When the body is very light

When the body is a point body

Solution

Question 3

Equal, opposite and acting on the same body

Equal, in the same direction and acting on same body

Equal, opposite and acting on different bodies

Equal, in same direction and acting on different bodies.

Solution

Question 4

Unity

Zero

Infinite

None of these

Solution

Question 5

2 : 3

1 : 2

2 : 1

3 : 2

Solution

Question 6

speed of $$\displaystyle 1{ ms }^{ -1 }$$

acceleration of $$\displaystyle 1{ ms }^{ -2 }$$

speed of $$\displaystyle 1{ kms }^{ -1 }$$

acceleration of $$\displaystyle 10{ ms }^{ -2 }$$

Solution

Question 7

$$40 N$$

$$20 N$$

$$4 N$$

$$2 N$$

Solution

Question 8

The body is definitely at rest

The body is definitely in the state of uniform motion

The body will be either at rest or in the state or uniform motion

None of these

Solution

Question 9

unity

zero

infinite

none of these

Solution

Question 10

Conservation of energy

Backward thrust of gases produced

Newton's first law of motion

Newton's third law of motion

Solution

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