An object is at rest at time $t = 0$. The variation with $t$ of the acceleration $a$ of the object is shown from $t = 0$ to $t = 20{\text{ s}}$.

What is the speed of the object when $t = 15{\text{ s}}$?

A.     ${\text{25 m}}\,{{\text{s}}^{ - 1}}$

B.     ${\text{50 m}}\,{{\text{s}}^{ - 1}}$

C.     ${\text{75 m}}\,{{\text{s}}^{ - 1}}$

D.     ${\text{100 m}}\,{{\text{s}}^{ - 1}}$

B

Think units.

If we want a speed then this can only be calculated from the area under the graph.