A ball is thrown straight upward. At the very top of its trajectory, what is true about its velocity and acceleration?
ABoth velocity and acceleration are zero
BVelocity is zero; acceleration is nonzero and directed downward
CVelocity is nonzero; acceleration is zero
DBoth velocity and acceleration are nonzero and directed downward
At the peak, the ball momentarily stops moving upward — its velocity is zero. But gravity does not stop acting. The acceleration due to gravity is approximately 9.8 m/s² downward throughout the entire flight, including at the peak. Zero velocity does not imply zero acceleration; confusing these two quantities is one of the most common kinematics errors.
Question 2 True / False
On a position-time graph, a steeper slope indicates a higher position.
TTrue
FFalse
Answer: False
On a position-time graph, the slope at any point equals the instantaneous velocity, not the position. A steep slope means the object is moving quickly; a flat (zero-slope) segment means it is momentarily at rest. The vertical height of the curve shows position, but steepness (slope) shows speed. Conflating slope with height is a classic graph-reading error.
Question 3 Short Answer
What is the difference between velocity and speed in one-dimensional kinematics, and why does the distinction matter?
Think about your answer, then reveal below.
Model answer: Speed is the magnitude of velocity — always non-negative. Velocity is signed: positive if moving in the chosen positive direction, negative if moving the other way. The distinction matters because displacement and direction of motion depend on the sign of velocity, not just its magnitude.
In 1D kinematics, we choose a positive direction (e.g., 'up' or 'to the right'). An object moving in the opposite direction has negative velocity but positive speed. This distinction becomes critical when computing displacements and identifying turning points: an object with velocity -10 m/s is moving fast — just in the negative direction.