Mechanics (Physics) (Part-2)

Total Questions: 49

21. Why does a cannon recoil after firing? [S.S.C. Online Graduation Level (T-I) 10.09.2016 (Shift-II)]

Correct Answer: (c) Newton's third law of motion
Solution:The retreat of a cannon after firing is an example of Newton's third law of motion
which states:
For every action, there is an equal and opposite reaction.
Explanation:

Action: When the cannon is fired, it exerts a force on the cannonball, pushing it forward at high speed.
Reaction: The cannonball exerts an equal and opposite force on the cannon, pushing it backward. This backward movement of the cannon is called recoil.

22. For every action, there is an equal and opposite reaction, is Newton's _______ . [S.S.C. Online CHSL (T-I) 8.01.2017 (Shift-I)]

Correct Answer: (c) Third Law
Solution:According to Newton's third law of motion, for every action, there is an equal and opposite reaction.
Explanation:
This means that:

Whenever one object exerts a force on a second object,
The second object exerts an equal and opposite force back on the first object.

Examples of Newton’s Third Law:

Cannon and Cannonball: When the cannon fires the cannonball forward (action), the cannon recoils backward (reaction).
Walking: When you push back on the ground with your foot (action), the ground pushes you forward (reaction), allowing you to move.
Balloon Rocket: When air rushes out of a balloon (action), the balloon flies in the opposite direction (reaction).
Jumping: You push down on the ground (action), and the ground pushes you up (reaction), allowing you to jump.

23. Rocket propulsion technology works on which of the following scientific principles? [S.S.C. JE Civil Exam 23.03.2021 (Shift-I)]

Correct Answer: (b) Newton's laws of motion
Solution:Rocket propulsion technology is based on Newton's third law of motion.

This law of Newton is also called the law of action and reaction.
In fact, it works on the principle of conservation of momentum.

24. It is difficult to fix a nail into a freely suspended wooden frame. Which law supports this statement? [S.S.C. Online Graduation Level (T-I) 9.08.2017 (Shift-II)]

Correct Answer: (c) Newton's third law
Solution:According to Newton's third law, every action has an equal and opposite reaction.
Explanation:
When you hit the nail with a hammer (action), the nail tries to push into the wood.
According to Newton’s Third Law, the nail (and wood) exerts an equal and opposite reaction force on the hammer.

Now, because the wooden frame is freely suspended (not fixed to anything), it moves backward instead of resisting the nail's entry.

25. Which law of motion states that when one substance exerts a force on another substance, the second substance immediately exerts a force back on the first? [S.S.C. Online Constable GD 2.03.2019 (Shift-II)]

Correct Answer: (d) Newton's third law of motion
Solution:Newton's third law of motion is also known as the action-reaction law.
  • It expresses that for every action there is an equal and opposite reaction.
  • That is, if one object exerts a force on another body, then that object or body also exerts the same force on the first object.

26. The movement of a horse-drawn carriage is an example of which principle of physics? [S.S.C. Online Constable GD 1.03.2019 (Shift-I)]

Correct Answer: (a) Newton's third law of motion
Solution:

The movement of a horse-drawn carriage is an example of Newton’s Third Law of Motion.

Explanation:

When the horse pulls the carriage forward, the following actions take place:

The horse pushes backward on the ground with its hooves (action).
The ground pushes forward on the horse with an equal and opposite force (reaction), causing the horse (and carriage) to move forward.

At the same time:

The horse exerts a forward force on the carriage through the harness.
The carriage exerts an equal and opposite backward force on the horse.

But because the force of the ground pushing the horse forward is greater than the carriage’s resistance, the whole system moves forward.

27. Which physical theory explains the generation of thrust by rocket engines, jet engines and deflating balloons? [S.S.C. Online CPO SI (T-I) 10.11.2022 (Shift-II)]

Correct Answer: (a) Newton's laws of motion
Solution:The generation of thrust by rocket engines, jet engines, and deflating balloons can be explained by Newton's third law of motion, also known as the law of action and reaction.

This law states that for every action, there is an equal and opposite reaction.

How it applies:

Rocket Engines:

Action: Hot gases are expelled backward at high speed.
Reaction: The rocket is pushed forward with equal force (thrust).

Jet Engines:

Action: Air is taken in, compressed, mixed with fuel, and exhaust is expelled backward.
Reaction: The jet moves forward.

Deflating Balloons:

Action: Air rushes out of the open end of the balloon.
Reaction: The balloon moves in the opposite direction.

28. Acceleration in a body by an unbalanced force is_______. [S.S.C. Online Stenographer 13.09.2017 (Shift-II)]

Correct Answer: (b) directly proportional to the force
Solution:Acceleration is the rate of change of velocity of an object with respect to time.

An object's acceleration is the net result of any and all forces acting on the object, as described by Newton's Second Law.

Newton's second law of motion can be formally stated as follows:

"The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object."

       f= ma

29. Which of the following statements is not correct regarding the gravitational force? [S.S.C. Online Constable GD 13.02.2019 (Shift-II)]

Correct Answer: (b) It is inversely proportional to the product of the masses of the objects.
Solution:

The correct relationship is that gravitational force is directly proportional to the product of the masses.

Newton's Law of Universal Gravitation

Isaac Newton's Law of Universal Gravitation describes the attractive force between any two objects with mass. The law states that this force is:

Directly proportional to the product of the two masses ( and ).

Inversely proportional to the square of the distance () between their centers.

This is represented by the formula:

where is the gravitational force, and is the gravitational constant.

Analyzing the Options

(a) It is the force responsible for the attraction of every object in the universe towards each other. This is a correct description of universal gravitation.

(b) It is inversely proportional to the product of the masses of the objects. This statement is incorrect. The force is directly proportional to the product of the masses.

(c) Newton relied on Kepler's theories in his research on the force of gravity. This is correct. Newton used Kepler's Laws of Planetary Motion to formulate his own law of gravity, explaining why planets orbit the sun in the way they do.

(d) It is inversely proportional to the square of the distance between the objects. This is correct, as stated in the inverse-square law component of Newton's equation.

30. In the Millikan's Oil Drop experiment, the oil drop is subjected to such forces whose nature does not fall under the category of________. [S.S.C. Online CPO SL. (T-I) 23.11.2020 (Shift-I)]

Correct Answer: (d) magnetostatic
Solution:In Millikan's oil drop experiment, the oil drop is subjected to such forces whose nature does not fall under the category of Magnetostatic.

Magnetic force is absent in the oil droplet experiment.
In 1913, the American physicist R. A. Millikan performed the pioneering oil-drop experiment to measure an electron's charge precisely.
He found that the charge on an oil droplet was always an integral multiple of an elementary charge 1.602 × 10⁻¹⁹ С.
Millikan's experiment established that electric charge is quantized.