Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 57

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Question 1
1 / -0

Choose the correct statement from the following:
Weightlessness of an astronaut moving in a satellite is a situation of

A
Zero $$g$$

B
No gravity

C
Zero mass

D
Free fall

Solution

Hint: Weight is a normal reaction force due to the contact of an object with the surface.
Part 1: Definition of free fall.
Free fall is the situation where only gravitational force is acting on a system or object.
Part 2: Weightlessness implies free fall.
Since the astronaut is not experiencing any counter normal reaction force to balance gravity and only gravitational force is acting on them. They are experiencing free fall.
Question 2
1 / -0

Rocket propulsion theory is analogues to-

A
Newton`s third law

B
Relative theory

C
First law of thermodynamics

D
none

Solution
Question 3
1 / -0

A bullet weighing $$50$$ gram leaves the gun with a velocity of $$30m/s$$.the ratio of their momentum is:

A
$$1:1$$

B
$$1:2$$

C
$$2:1$$

D
$$1:3$$

Solution
Question 4
1 / -0

A truck is moving on a frictionless surface with uniform velocity of $$10\,m{s^{ - 1}}$$. A leak occurs in the water tank of the truck at the rate of $$2\,{kg^{ - 1}}$$. What is the speed of truck after $$50 \ s$$, if the mass of truck is $$100\,kg$$ and mass of water in the truck initially was $$100\,kg$$?

A
$$20\,m{s^{ - 1}}$$

B
$$10\,m{s^{ - 1}}$$

C
$$5\,m{s^{ - 1}}$$

D
None of these

Solution
Question 5
1 / -0

Principle of rocket is based on Newton's $$..........$$ law of motion.

A
first

B
second

C
third

D
none

Solution
Question 6
1 / -0

A force of $$50\ N$$ is required to push a car on a level road with constant speed of $$10\ ms^{-1}$$. The mass of the car is $$500\ kg$$. What forces should be applied to make the car accelerate at $$1\ ms^{-2}$$.

A
$$450\ N$$

B
$$500\ N$$

C
$$550\ N$$

D
$$2500\ N$$

Solution

Hint: Newton's second law of motion suggests that the net force applied to an object produces a proportional acceleration.
Step 1: Obtain an expression for the net force acting on the car.
When the car travels with a constant speed, it is given that the force applied against friction is equal to $$50N$$. Now, the net force on the car to make it travel with an acceleration equal to $$1m{{s}^{-2}}$$ can be represented as:
$${{F}_{net}}=F'-50$$
Let this be equation 1.
Here, $${{F}_{net}}$$ denotes the net force on the car and $$F'$$ represents the force with which the car needs to be pushed for it to travel with an acceleration of $$1m{{s}^{-2}}$$.
Step 2: Apply Newton's second law of motion to obtain the required force.
We are given that mass of the car is $$500kg$$ and the acceleration with which the car has to travel is $$1m{{s}^{-2}}$$.
Newton's second law of motion suggests that the net force applied to an object produces a proportional acceleration. Mathematically,
$${{F}_{net}}=ma$$
Let this be equation 2.
Substituting the value of $$m$$, $$a$$ and equation 1 in equation 2,
$$F'-50=ma$$
$$F'-50=500\times 1$$
$$F'=500+50$$
$$F'=550N$$
Final step: Therefore, the force with which the car needs to be pushed for it to travel with an acceleration of $$1m{{s}^{-2}}$$ is $$550N$$.
Question 7
1 / -0

An object maintains its motion under the continuous application of ________force

A
An unbalanced

B
A balanced

C
A strong

D
A weak

Solution

An object maintains its motion under the continuous application of an unbalanced force, hence option A is correct.
Question 8
1 / -0

What happens when some children try to push a box on a rough floor?

A
The box will move regardless of the force given

B
The box moves with a little force

C
The box does not move with a small force

D
None of these

Solution

Friction opposes the relative motion between two surfaces in contact. It acts on both surfaces. When some children try to push a box on a rough floor box with a small force, the box does not move because of friction acting in a direction opposite to the push. This friction force arises between two surfaces in contact. It balances the pushing force and therefore the box does not move.
Question 9
1 / -0

Which of the following uses the principle of conservation of momentum?

A
Motion of rockets and jet engines

B
Ballon moves upwards when burst or when air is expelled out of it

C
Gun recoils after firing

D
All of these

Solution

In the air-filled balloon, balloon, and air inside form a kind of system. Initially when the system is at rest, so the momentum of the system is also zero. As soon as the balloon is set free air escapes out with some great velocity, balloon moves forward in the direction opposite to air rushing out, before firing both gun and bullet are at rest, therefore momentum of the system is zero. When the bullet is fired the bullet moves forward and gun recoils back. Rockets and jet engines also work on the law of conservation of momentum. In these hot gases produced by burning of fuel rush out with large momentum, Due to this, these machines gain an equal and opposite momentum. This momentum enables the rockets and jet engines with very high velocities, hence option $$D$$ is correct.
Question 10
1 / -0

What is the action reaction pair when we walk on the floor?

A
Air resistance, muscular force

B
Air resistance, force applied by road on your feet

C
Your feet exerts force on road, road reverts equal force back

D
None of these

Solution

When you walk, you push the road below backwards. The road exerts an equal and opposite force on your feet to make you move forward, hence option $$C$$ is correct.