Physics - NLM Question with Solution | TestHub

A net force is required whenever the velocity changes (in magnitude or direction) - i.e. whenever there is acceleration.

(A) The car's speed changes from 0 to 80 km/hr - accelerated, so a net force acts. Correct.

(B) Constant speed, straight-line lowering - no acceleration, no net force needed. Wrong.

(C) The skater slows from 10 m/s to 5 m/s - deceleration, so a net force acts. Correct.

(D) Straight line with constant speed - no acceleration, no net force. Wrong.

Correct options: (A), (C).