Question 4
The displacement–time graph of an object is shown below. When the motion began, the object was already 12 m from the starting point.
| t (s) | 0 | 4 |
|---|---|---|
| s (m) | 12 | 0 |
What is the object's velocity, and what does it tell us?
The right answer is the one marked above.
−3 m s-1; the object is moving back towards its starting point. The line slopes downwards, so the gradient is negative:
velocity = (0 − 12) m ÷ (4 − 0) s = −3 m s-1
The displacement falls from 12 m to 0, so the object travels back towards its starting point and reaches it at t = 4 s. The negative sign shows the direction of the motion, not that the velocity is dropping — its magnitude stays at 3 m s-1 throughout.