Question

Which of the following statements describes a scenario where an object started moving without any force applied on it?

i) The balloon filled with helium is going upward with increasing speed.

ii) A ball dropped from a height going downwards with increasing speed.

iii) Movement of an motorcycle

• A. Only (i) and (iii)
• B. Only (i)
• C. All the three statements
• D. None of these

Answer 1

Answer: (D)

None of these

Answer 2

According to Newton's first law of motion, an object at rest remains at rest unless acted upon by a net external force. Starting to move from a state of rest means changing the state of motion (from zero velocity to non-zero velocity), which implies acceleration. According to Newton's second law of motion, acceleration is directly proportional to the net force acting on the object ($\vec{F}_{net} = m\vec{a}$). Therefore, a net force is always required to start an object moving from rest.

Let's analyze each statement:

i) The balloon filled with helium is going upward with increasing speed. This means the balloon is accelerating upwards. For this to happen, there must be a net upward force acting on the balloon (the buoyant force from the air must be greater than the gravitational force and any air resistance). Thus, force is applied.

ii) A ball dropped from a height going downwards with increasing speed. This means the ball is accelerating downwards due to gravity. Gravity is a force acting on the ball. For the speed to increase, there is a net downward force (gravity minus air resistance). Thus, force is applied.

iii) Movement of a motorcycle. To start moving from rest, a motorcycle's engine generates power that is converted into a force (ultimately through friction between the tires and the road) that propels the motorcycle forward. This is a force causing the motion. Thus, force is applied.

In all three scenarios, the objects are either starting to move from rest or are accelerating, both of which require a net force according to Newton's laws of motion. Therefore, none of the statements describe a scenario where an object started moving without any force applied on it.