Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 51

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Weekly Quiz Competition

Question 1
1 / -0

A rocket with a lift-off mass $$3.5\times {10}^{4}\ kg$$ is blasted upwards with an initial acceleration of $$10m{s}^{-2}$$. Then the initial thrust of the blast is:

A
$$3.5\times {10}^{5}N$$

B
$$7.0\times {10}^{5}N$$

C
$$14.0\times {10}^{5}N$$

D
$$1.75\times {10}^{5}N$$

Solution

According to the second law of Newton-
$$F = ma$$
$$F$$; Force or thrust
$$m$$; the mass of the object
$$a$$; acceleration of the object

$$\Rightarrow F = (3.5 \times 10^4) \times 10$$

$$\Rightarrow F = 3.5 \times 10^5\ N$$
Question 2
1 / -0

A gun weighing $$10\ kg$$ fires a bullet of $$30\ g$$ with a velocity $$330\ m/s$$ With what velocity does the gun recoil?

A
$$2\ m/s$$

B
$$1\ m/s$$

C
$$0\ m/s$$

D
$$3\ m/s$$

Solution

Given,
Mass of the gun, $$m_g=10\ kg$$
Mass of the bullet, $$m_b=30\ g=0.03\ kg$$
Velocity of the bullet, $$v_b=330m/s$$
Velocity of the gun, $$v_g$$
By applying the conservation of linear momentum,
$$m_gv_g=m_bv_b$$
$$10\times v_g=0.03\times 330$$
$$v_g=1\ m/s$$
Question 3
1 / -0

The velocity acquired by a mass $$m$$ in travelling a certain distance $$d$$ starting from rest under the action of a constant force is directly proportional to:

A
$$\sqrt {m}$$

B
$$m^{o}$$

C
$$\dfrac {1}{\sqrt {m}}$$

D
$$m$$

Solution

Force,
$$ F=ma $$
$$ F\,\propto \,m $$
Hence, force is directly proportional to $$m$$
Question 4
1 / -0

According to Newton's third law action is always equal and opposite to the reaction, a horse can pull a cart because it applies a ______.

A
Force on cart

B
Force on ground

C
Both A and B

D
None of these

Solution

When horse applies force on ground in backward direction then ground also applies equal force in forward direction on the horse which helps horse to move forward.according to Newton Third Law.So option B is correct.
And at the same time horse applies force on ropes connected to cart so horse also applies force on cart which moves the cart.
Question 5
1 / -0

A $$10\ N$$ force applied on a body produces in it an acceleration of $$2\ m{ s }^{ -2 }$$. The mass of the body is

A
$$2\ kg$$

B
$$5\ kg$$

C
$$10\ kg$$

D
$$20\ kg$$

Solution

Applying Newton’s second law of motion,
$$F=ma$$
$$\Rightarrow a=\dfrac{F}{m}$$ and $$m=\dfrac{F}{a}$$
Here, $$F=10\ N$$ and $$a=2\ m/{s}^{2}$$
$$\Rightarrow m=\dfrac{10}{2}=5\ kg$$
Option $$-B$$ is correct.
Question 6
1 / -0

Fill in the blanks.
At least _____________ objects must be present to experience a gravitational force.

A
1

B
2

C
3

D
4

Solution

Gravitational force is the mutual attraction between any two objects. When there are more than two objects, all the possible pairs of the objects will experience the gravitational force.
So, we need at least two objects to realize the gravitational force.
Question 7
1 / -0

Swimming is based on Newton's:

A
First law of motion

B
second law of motion

C
third law of motion

D
law of gravitation

Solution

When swimmer apply force on the water , then reaction force act on the man due to water. This force on the man drive man forward in the water.
This is an example of Newton’s 3rd law of motion.
Question 8
1 / -0

Which of the following objects experience balanced forces?

A
A ball dropping vertically

B
A car accelerating uniformly from rest

C
A trolley moving at a constant velocity down an inclined plane

D
A plane flying in a circle with constant speed

Solution

In case(c) Trolley is moving at constant speed so no change in velocity means acceleration is zero.
$$a=0$$
Now according to Newton's second law
$$F=ma$$
$$F=m\times0$$
$$F=0$$
So it experience no net force or the forces on it are balanced.
Question 9
1 / -0

A person holding a rifle (mass of person and rifle together is 100 kg) stands on a smooth surface and fires 10 shots horizontal, in 2 s. Each bullet has a mass of 10 g with a muzzle velocity of $$800{ ms }^{ -1 }.$$ The final velocity acquired by the person and the average force exerted on the person are

A
$$-0.8{ ms }^{ -1 },16N$$

B
$$-0.8{ ms }^{ -1 },8N$$

C
$$-1.6{ ms }^{ -1 },16N$$

D
$$-1.6{ ms }^{ -1 },8N$$

Solution

$$P ( initial ) = P ( final )$$

$$0 = n \times m \times u + ( M - n \times m ) \times v$$

where: $$n = 10, m = 10 g = 0.01 kg, u = 800 m/s, M = 100 kg$$

$$0 = 10 \times 0.01 kg \times 800 m/s + ( 100 kg - 10 \times 0.01 kg ) \times v$$

$$v = - \dfrac{80 kgm/s} {99.9 kgm/s}$$

$$v = -0.8 m/s$$

Then : $$F =\dfrac{\Delta P}{\Delta t}= \dfrac{ 10 \times 0.01 kg \times 800 m/s }{ 5 s} = 16 N$$
Question 10
1 / -0

A force of 15N acts separately on two bodies of masses 3kg and 5kg. The ratio of the acceleration produced in the two cases will be

A
$$5:3$$

B
$$3:5$$

C
$$8:15$$

D
$$15:8$$

Solution

Given,
$$F=15N$$
$$m_1=3kg$$
$$m_2=5kg$$
We know that, $$F=ma$$
$$a=\dfrac{F}{m}$$
The force acted on the bodies is same,
So, $$\dfrac{a_1}{a_2}=\dfrac{m_2}{m_1}=\dfrac{5}{3}$$
Ratio, $$a_1:a_2=5:3$$
The correct option is A.

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Re-Attempt Weekly Quiz Competition

Forces and Laws of Motion Test - 51

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Forces and Laws of Motion Test - 51

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Question 1

$$3.5\times {10}^{5}N$$

$$7.0\times {10}^{5}N$$

$$14.0\times {10}^{5}N$$

$$1.75\times {10}^{5}N$$

Solution

Question 2

$$2\ m/s$$

$$1\ m/s$$

$$0\ m/s$$

$$3\ m/s$$

Solution

Question 3

$$\sqrt {m}$$

$$m^{o}$$

$$\dfrac {1}{\sqrt {m}}$$

$$m$$

Solution

Question 4

Force on cart

Force on ground

Both A and B

None of these

Solution

Question 5

$$2\ kg$$

$$5\ kg$$

$$10\ kg$$

$$20\ kg$$

Solution

Question 6

1

2

3

4

Solution

Question 7

First law of motion

second law of motion

third law of motion

law of gravitation

Solution

Question 8

A ball dropping vertically

A car accelerating uniformly from rest

A trolley moving at a constant velocity down an inclined plane

A plane flying in a circle with constant speed

Solution

Question 9

$$-0.8{ ms }^{ -1 },16N$$

$$-0.8{ ms }^{ -1 },8N$$

$$-1.6{ ms }^{ -1 },16N$$

$$-1.6{ ms }^{ -1 },8N$$

Solution

Question 10

$$5:3$$

$$3:5$$

$$8:15$$

$$15:8$$

Solution

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