6.1 Quantity Represented by the Gradient of a Graph (Part 2)


(B) Speed – Time Graph
1. The gradient of a speed-time graph is the rate of change of speed or acceleration.




2.


(a) From O to P: Gradient = positive → (Speed of object increasing or accelerating).

(b) 
From P to Q: Gradient = 0 → (Object is moving at uniform speed).

(c) 
From Q to R: Gradient = negative → (Speed of object decreasing or decelerating).


Example:


The diagram above shows the speed-time graph of a moving car for 5 seconds. Find
(a) the rate of speed change when the car travel from X to Y.
(b) the rate of speed change when the car travel from Y to Z.
 
Solution:
(a)
Rate of speed change when the car travels from X to Y
= Gradient
=y2y1x2x1=52040=154ms2Negative gradient indicatesthat the speed is decreasing.

(b)
Rate of speed change when the car travels from Y to Z
= Gradient
=y2y1x2x1=10554=5ms2