A car starts from rest

PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A car starts from rest, accelerates uniformly and reaches a speed of

20\,\text{m/s}

4\,\text{s}

, then continues at this speed for the next

3\,\text{s}

. Which of the following gives the correct qualitative shape of the velocity–time graph for this motion? (a) A horizontal line at

20\,\text{m/s}

from

t=0

4\,\text{s}

, followed by a straight line sloping downward to

(7\,\text{s},0)

. (b) A straight line sloping upward from

(0,0)

(4\,\text{s},20\,\text{m/s})

followed by a horizontal line at

20\,\text{m/s}

up to

7\,\text{s}

. (c) A curved line rising from

(0,0)

(4\,\text{s},20\,\text{m/s})

and then remaining horizontal at

20\,\text{m/s}

till

7\,\text{s}

. (d) A straight line sloping upward from

(0,0)

(4\,\text{s},20\,\text{m/s})

and continuing the same slope to

(7\,\text{s},40\,\text{m/s})