Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 16

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Weekly Quiz Competition

Question 1
1 / -0

In above figure, two boys A and B are shown applying force on a block. If the block moves towards the right, which one of the following statements is correct?

A
Magnitude of force applied by A is greater than that of B.

B
Magnitude of force applied by A is smaller than that of B.

C
Net force on the block is towards A.

D
Magnitude of force applied by A is equal to that of B.

Solution

In right direction total force $$= A-B$$
Since, block is moving in right direction, net force in right direction must be positive.
therefore, $$A-B > 0$$
$$A> B$$
Question 2
1 / -0

A girl is pushing a box towards east direction. In which direction should her friend push the box so that it moves faster in the same direction?

A
North

B
South

C
East

D
West

Solution

Towards East,
As both of them would be applying the force in the same direction, so that resultant force will be more.
Question 3
1 / -0

A $$500 \ gm$$ gun fires a $$2 \ gm$$ bullet with a muzzle velocity of $$1600 \ ms^{-1}$$. The velocity of the gun is:

A
$$-0.64 \ ms^{-1}$$

B
$$-6.4 \ ms^{-1}$$

C
$$6.4 \ ms^{-1}$$

D
$$0.64 \ ms^{-1}$$

Solution

Given , mass of gun $$m_g = 500 \ gm = 0.5 \ kg$$
mass of bullet $$m_b = 2 \ gm = 0.002 \ kg$$
final velocity of bullet $$v_b=1600 \ ms^-1$$

Let $$v_g$$ be the final velocity of gun
Since, the gun and bullet are initially at rest, their initial velocities are $$u_b=u_g=0$$.

Using linear momentum conservation:
$$m_bu_b+m_gu_g=m_bv_b +m_gv_g$$

$$0=0.002 \times 1600 + 0.5 \times v_g$$

$$\Rightarrow v_g = -6.4\ m/s$$
Question 4
1 / -0

A boy of mass 40 kg jumps off a boat with a velocity of $$3ms^{-1}$$ . With what momentum does the boat move ?

A
$$-210kg.ms^{-1}$$

B
$$-120kg.ms^{-1}$$

C
$$-125kg.ms^{-1}$$

D
$$-215kg.ms^{-1}$$

Solution

Using momentum conservation,

$$m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2 $$
$$m_1=mass$$ $$of$$ $$boy$$ $$m_2=mass $$ $$of $$ $$boat$$
$$m_1=40kg$$ $$,v_1=3\ m/s$$ $$u_1=0$$ $$u_2=0$$
$$\Rightarrow 40\times 0+m_2 \times 0= 40 \times 3+m_2\times v_2$$
$$\Rightarrow 0+0= 120+P\:boat$$
$$0 = P\:boat + 120$$
$$P\:boat = -120\ kgm/s$$
Question 5
1 / -0

What is the magnitude of the pseudo force on a driver by the racing car he operates, as it accelerates horizontally along a straight line from rest to $$60\ ms^{-1}$$ in $$ 8.0\ s$$?
(mass of driver $$= 80\ kg)$$

A
$$0.6\ kN$$

B
$$0.78\ kN$$

C
$$1.4\ kN$$

D
$$1.0\ kN$$

Solution

Using equations of motion to calculate acceleration and subsequently force :
Initial velocity,
$$u=0 ms^{-1}$$
Final velocity,
$$v=60 ms^{-1}$$
Time, $$t= 8\ s$$
Using the equation of motion,
$$v=u+at$$ (where $$a$$ is the acceleration)
$$\Rightarrow 60 = 0 + 8a$$
$$\Rightarrow a = \dfrac{ 60 }{ 8 }$$
$$\Rightarrow a = 7.5 ms^{-2}$$
According to the newton's second law-
$$F = ma$$
$$m = 80\ kg$$; mass of the driver
$$\Rightarrow F = 80 \times 7.5$$
$$\Rightarrow F = 600\ N$$
Question 6
1 / -0

When an athlete takes part in a long jump he runs for a while and then jumps. This is because:

A
inertia of motion helps him to take a longer jump.

B
running for a time makes him alert.

C
it helps him to focus on the point of jump.

D
he can apply more force for the jump after running.

Solution

The inertia helps him to retain his horizontal speed and hence the athlete can jump with a greater horizontal velocity to cover a longer distance.
Question 7
1 / -0

Newton's second law of motion gives

A
magnitude of force

B
velocity of the object

C
concept of inertia

D
all the above

Solution

According to Newton's second law if a body is acceleration with acceleration $$a$$ and mass of a body is $$M$$ then the force will on the body equal to $$F=ma$$.
Hence Option A
Question 8
1 / -0

Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied.

A
Force in the direction opposite to the motion is zero

B
Force in the direction opposite to the motion is greater

C
Both are Pushing with equal and opposite force

D
Force in the direction of motion is greater.

Solution

Two persons are applying forces on two opposite sides of a moving cart, but the cart still moves with the same speed in the same direction.
This leads us to a conclusion that both are applying an equal magnitude force, and the direction of force by both of them is opposite to each other.
As a result both the forces cancel out each other(Resultant force =0) and the cart continues to move with the same speed in the same direction.
Question 9
1 / -0

Water sprinkler used for grass lawns begins to rotate as soon as the water is supplied. It is based on which law?

A
Newton's first law of motion

B
Newton's second law of motion

C
Newton's third law of motion

D
First law of thermodynamics

Solution

The working of the rotation of sprinkler is based on third law of motion.
As the water comes out of the nozzle of the sprinkler, an equal and opposite reaction force comes into play. So the sprinkler starts rotating.
Question 10
1 / -0

A boat with a sail, has an electric fan inside. When the fan starts, the boat

A
Cannot move

B
Can move

C
Moves depending on wind directions

D
Moves depending on the speed of the fan

Solution

When the fan starts, the fan will throw the air on the sail, which will take the boat forward.
But due to reaction force by the fan boat will go back.
Ultimately boat will stay at its point.

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Forces and Laws of Motion Test - 16

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Forces and Laws of Motion Test - 16

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Question 1

Magnitude of force applied by A is greater than that of B.

Magnitude of force applied by A is smaller than that of B.

Net force on the block is towards A.

Magnitude of force applied by A is equal to that of B.

Solution

Question 2

North

South

East

West

Solution

Question 3

$$-0.64 \ ms^{-1}$$

$$-6.4 \ ms^{-1}$$

$$6.4 \ ms^{-1}$$

$$0.64 \ ms^{-1}$$

Solution

Question 4

$$-210kg.ms^{-1}$$

$$-120kg.ms^{-1}$$

$$-125kg.ms^{-1}$$

$$-215kg.ms^{-1}$$

Solution

Question 5

$$0.6\ kN$$

$$0.78\ kN$$

$$1.4\ kN$$

$$1.0\ kN$$

Solution

Question 6

inertia of motion helps him to take a longer jump.

running for a time makes him alert.

it helps him to focus on the point of jump.

he can apply more force for the jump after running.

Solution

Question 7

magnitude of force

velocity of the object

concept of inertia

all the above

Solution

Question 8

Force in the direction opposite to the motion is zero

Force in the direction opposite to the motion is greater

Both are Pushing with equal and opposite force

Force in the direction of motion is greater.

Solution

Question 9

Newton's first law of motion

Newton's second law of motion

Newton's third law of motion

First law of thermodynamics

Solution

Question 10

Cannot move

Can move

Moves depending on wind directions

Moves depending on the speed of the fan

Solution

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