Force and Laws of Motion MCQs

Q1. A heavy bronze statue has stood in a museum courtyard for a century without budging. What single property best explains why it stays put on its own?

• A.The pedestal grips the base and refuses to let it slide
• B.Air pressure pins it down from all directions equally
• C.Its great age has fused it to the ground over time
• D.Its inertia of rest, the tendency of a body to remain stationary until an external unbalanced force acts

Answer: D. Its inertia of rest, the tendency of a body to remain stationary until an external unbalanced force acts

An object at rest stays at rest until an unbalanced force acts on it. The statue's tendency to keep its stationary state is its inertia of rest, so it remains undisturbed for years.

Q2. A librarian notices that a thick dictionary left on a shelf yesterday is in the exact same spot today. Which idea accounts for the book holding its position?

• A.The shelf slowly pushes the book back to where it belongs
• B.Dust settling on the cover holds the book in place
• C.Books are too light to move themselves anywhere
• D.Inertia of rest keeps the book stationary because no unbalanced force has acted to move it

Answer: D. Inertia of rest keeps the book stationary because no unbalanced force has acted to move it

By the first law a stationary body remains at rest unless acted on by an unbalanced force. With no such force, the dictionary's inertia of rest keeps it exactly where it was placed.

Q3. At a dinner party a performer whips a long tablecloth from beneath a laid-out service of plates and glasses, leaving them undisturbed. What makes this possible?

• A.The crockery's inertia of rest, since the rapid pull lasts too short a time to give the dishes enough impulse to move
• B.The cloth gently raises the dishes and lowers them again
• C.A thin film of wax under each plate cements it down
• D.Static charge on the cloth pulls the dishes downward

Answer: A. The crockery's inertia of rest, since the rapid pull lasts too short a time to give the dishes enough impulse to move

Because the cloth is yanked away very fast, friction acts on the dishes for too short a time to overcome their inertia of rest, so they barely shift and remain on the table.