A toy car of mass moves on a smooth horizontal table
PHYSICS · Subjective · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A toy car of mass 1kg moves on a smooth horizontal table. The horizontal forces acting on the car change in three successive time intervals, as described below.
Interval I (first 4s): two opposite horizontal forces of 12N each act on the car.
Interval II (next 3s): the force acting towards the east remains 12N, while the opposing force drops to 7N.
Interval III (next 5s): only the 12N eastward force continues to act; no force acts in the opposite direction.
The car is initially at rest at t=0.
(a) For each interval, calculate the magnitude and direction of the net horizontal force on the car and state whether the forces are balanced or unbalanced.
(b) For each interval, predict qualitatively (increase, decrease, or constant) the car’s speed.
(c) On the axes provided in your answer book, sketch a qualitative velocity–time graph for the entire 12s motion. Clearly mark the three intervals and indicate the nature of the motion in each.
(d) Identify the exact instants (if any) during which the car moves with uniform velocity and justify your answer.