Graphs 3
4 marks · NormalThe distance–time graph below shows the journey of Sarah walking from home to the park and then returning home.
a) Find Sarah's speed (in km/h) as she walks from home to the park.
b) For how long did Sarah rest at the park?
c) Find Sarah's speed (in km/h) as she walked home from the park.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 4 km/h
(b) 0.5 hours
(c) 4 km/h
Common mistakes: Mixing up time intervals.; Using distance from home incorrectly after resting.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct calculation of speed as gradient: km/h.
B1 (b) · 1 mark · Correctly finds resting time (flat part): 1.5 − 1 = 0.5 hours.
M1 (c) · 1 mark · Calculates speed for return: km/h using correct values. (follow-through)
A1 (c) · 1 mark · Correct unit for speed and final value. (follow-through)
Worked solution
a) Speed = gradient = (change in distance) / (change in time) = (4−0) / (1−0) = 4 km/h.
b) Sarah rests from 1 hour to 1.5 hours: 1.5 − 1 = 0.5 hours.
c) Return journey: gradient = (0−4) / (2.5−1.5) = (−4)/1 = −4 km/h (speed is 4 km/h).