Newton's Laws — Set 5

Correct Answer: B. Isaac Newton

Isaac Newton published his laws of motion and universal gravitation in this monumental work in 1687. It laid the foundation for most of classical mechanics. The full title is 'Philosophiæ Naturalis Principia Mathematica'.

Correct Answer: B. Zero acceleration

Balanced forces have a resultant sum of zero, meaning they cancel each other out. Consequently, there is no change in the object's velocity or state of motion. The object remains either at rest or continues moving at a constant velocity.

Correct Answer: C. No external force acts

The Law of Conservation of Momentum applies when the net external force on a system is zero. Internal forces within the system do not change the total momentum. This principle is vital for analyzing collisions and explosions in physics.

Correct Answer: C. Static friction being higher

Static friction, which opposes the start of motion, is generally stronger than kinetic friction. The horse must overcome this initial resistance to set the cart in motion. Once moving, less force is required to maintain a constant speed.

Correct Answer: B. Second Law

The Second Law relates force and acceleration to the mass, which represents the quantity of matter. It allows mass to be measured by observing how an object responds to a known force. Mass is the constant of proportionality in the F = ma equation.

Correct Answer: A. Action and reaction are on different bodies

Action and reaction forces act on two different objects, so they never cancel each other out. Even though they are equal and opposite, they cause accelerations on different bodies. This is why a person can push a wall even though the wall pushes back.

Correct Answer: B. Force

Force is defined as the rate of change of momentum (dp/dt). Therefore, the slope of a graph showing momentum over time gives the instantaneous force acting on the body. This is a common way to visualize Newton's Second Law.

Correct Answer: D. Sand increases the time of impact

Sand is soft and yields, which increases the time it takes for the person's momentum to reach zero. According to the Second Law, increasing the time reduces the impact force acting on the body. Cemented floors stop the motion almost instantly, resulting in a much higher force.

Correct Answer: D. Opposite to motion

Kinetic friction always acts in a direction that opposes the relative sliding motion between surfaces. It works to slow down the object and eventually bring it to a stop. This force converts kinetic energy into thermal energy through heat.

Correct Answer: A. Inertia

Inertia is the property of a body by virtue of which it resists any change in its state. It is a fundamental concept introduced in Newton's First Law. This property is directly proportional to the mass of the object.