7.3.3 Graphs of Motion, SPM Paper 2 (Long Questions)

Question 7:

The diagram above shows the speed-time graph of a moving object for 15 seconds. Find

(a) the speed of the object at t = 9s.

(b) the distance travel by the object for the first 12 seconds.

Solution:
(a)

The speed of the object at t = 9s is 6 ms^-1

(b)

Distance travel by the object for the first 12 seconds

= Area under the speed-time graph

= Area of triangle

= ½ × 12 × 8

= 48 m

Question 8:

The diagram above shows the speed-time graph of a moving object for 15 seconds.

(a) Find the time interval when the object moves with constant speed.

(b) Find the acceleration from t = 6 s to t = 12 s.

(c) State the time when the object is stationary.

Solution:
(a)

Time interval when the object moves with constant speed

= 12 – 6

= 6 s

(b)

\begin{array}{l} Acceleration from t = 6 s to t = 12 s \\ = Gradient of speed-time graph \\ = \frac{6 - 6}{12 - 6} \\ = 0 {ms}^{- 2} \leftarrow \begin{array}{l} The moving object is moving \\ at a uniform speed \end{array} \end{array}

(c)

Time when the object is stationary is at 15 s.