A van starts from rest and its velocity changes according to the following schedule:…

PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A van starts from rest and its velocity changes according to the following schedule: • From

t=0

t=4\,\text{s}

, the velocity increases uniformly from

0

20\,\text{m\,s}^{-1}

. • From

t=4\,\text{s}

t=8\,\text{s}

, the velocity remains constant. • From

t=8\,\text{s}

t=12\,\text{s}

, the velocity decreases uniformly from

20\,\text{m\,s}^{-1}

4\,\text{m\,s}^{-1}

. (i) Sketch a velocity–time graph that represents the above motion. (ii) Calculate the instantaneous acceleration at

t=3\,\text{s}

t=6\,\text{s}

, and

t=10\,\text{s}

. (iii) For which time interval(s) is the acceleration zero? Give a physical interpretation of this result.