Question

A standing passenger falls backwards when the bus starts suddenly.

1. Explain why this happens?

2. Which Newtons law gives the above concept. State the law.

3. Obtain an expression for force using Newtons law.

Answer 1

1. Due to inertia of rest, the body continues in the state of rest.

2. Newtons first law:
Everybody continues in its state of rest or of uniform motion along a straight line unless it is compelled by an external unbalanced force to change that state:

3. Consider a body of mass ‘m’ moving with a momentum \(\vec p\) . Let \(\vec F\)  be the force acting on it for time internal ∆t. Due to this force the momentum is changed from \(\vec p\) to p + ∆p. Then according to Newtons second law, we can write

Where K is a constant pf proportionality. When we take the limit ∆t → 0, we can write