MCQ & Solution - Force and Laws of Motion | Science Class 9 PDF Download

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Multiple Choice Questions (MCQs)

This happens due to inertia of rest. The passengers' bodies are at rest, and when the bus moves suddenly, their lower bodies move with the bus, but their upper bodies resist the motion, causing them to fall backward.

By running, the athlete gains momentum, which helps him cover a longer distance in the jump. This is due to inertia of motion, which keeps the body moving in the same direction.

The rider's body is initially at rest. When the horse starts moving suddenly, the lower part of the rider's body moves forward with the horse, while the upper part tends to remain at rest due to inertia of rest, causing the rider to fall backward. 

Inertia is the tendency of an object to resist any change in its state of motion. This means an object at rest stays at rest, and an object in motion continues moving in a straight line unless an external force acts on it.

Newton’s First Law states that an object remains in its state of rest or uniform motion unless acted upon by an external force. This explains the concept of force qualitatively (without involving equations).

A Newton (N) is defined as the force required to accelerate a 1 kg mass by 1 m/s² (1 N = 1 kg·m/s²).

According to Newton’s Second Law of Motion, force is given by:$\mathrm{ F}=m\times aF\; =\; m\; \backslash times\; a$
Since the mass remains the same, the ratio of forces is equal to the ratio of accelerations:$F1 :F2=a\mathrm{1 }:a2$
$\mathrm{<span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;"><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">=\; 1.8 </span><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">: </span><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">1.2</span></span>}$
$\mathrm{<span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;"><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">=</span><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">3 </span><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">: </span><span\; style="background-color:\; transparent;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 18px;\; color:\; black;">2</span></span>}$
So, the correct answer is (d) 3 : 2.

Newton’s Second Law states that force (F) = mass (m) × acceleration (a). This equation quantifies force, making it the correct answer.

According to Newton’s Second Law, acceleration occurs when a net force acts on an object. When the resultant force becomes zero, the object stops accelerating and moves at a constant velocity. 

Newton’s Third Law states that for every action, there is an equal and opposite reaction. When the cannon fires a projectile forward, it experiences an equal force pushing it backwards, causing recoil.

A rocket expels gases at high speed in one direction, and by the law of conservation of momentum, the rocket moves in the opposite direction. This is based on Newton’s Third Law but specifically follows the principle of momentum conservation. 

From Newton’s Second Law: $F=m\times aF\; =\; m\; \backslash times\; a$
Force (F) has units of mass (kg) × acceleration (m/s²), which simplifies to kg·m/s², also known as a Newton (N).

According to Newton’s Second Law

where $pp$ is momentum ($p=m\times vp\; =\; m\; \backslash times\; v$). 

This means that the force acting on an object is equal to the rate of change of its momentum.

From Newton’s Second Law, acceleration occurs only when a net force is applied. Acceleration does not always mean an increase in speed—it could mean a change in velocity (direction) as well.

Newton’s Second Law states:$\mathrm{ F}=m\times aF\; =\; m\; \backslash times\; a$

This means acceleration (a) is directly proportional to force (F) and inversely proportional to mass (m). Hence, the correct answer is (a) The force on the object.