Distance-time graphs
5 marks · NormalA student times a remote-control car moving along a straight track. The car starts from rest at point A and moves at a steady speed until it reaches point B, 40 m away. It takes 25 seconds to get from A to B.
Calculate the average speed of the car as it moves from A to B. Give your answer in m/s.
After stopping at B for 15 seconds, the car returns with the same average speed to A. Draw the distance–time graph for the whole journey from A to B to A, labelling axes with units and marking the time points where the car changes direction or is stationary.
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) 1.6 m/s
(b) — · must show Y-axis labelled distance (m), X-axis labelled time (s), first section: straight line from (0,0) to (25,40), steady slope, horizontal line from (25,40) to (40,40), showing car stopped, straight declining line from (40,40) to (65,0), return to A
Common mistakes: swapping distance and time; not labelling axes on graph; not including stationary period
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitute correct values into speed = distance/time
A1 (a) · 1 mark · Calculates correct value with correct unit (1.6 m/s)
B1 (b) · 1 mark · Axes correctly labelled with units (distance in m, time in s)
B2 (b) · 1 mark · Graphs outbound journey A to B (0,0) to (25,40) as straight line
B3 (b) · 1 mark · Shows stationary period at B, then straight return to A ending at (65,0)
Worked solution
a) To calculate the average speed:
b) The graph should: - Start at (0,0), increase steadily to (25,40) (outbound journey) - Stay flat from (25,40) to (40,40) (stationary) - Decline steadily from (40,40) to (65,0) (return journey) - Y-axis: distance (m); X-axis: time (s).