What is the acceleration?

–0.4 m/s2

–0.2 m/s2

0.2 m/s2

0.4 m/s2

We are asked to solve for the acceleration with the given graph in the problem. Let us recall that the formula for acceleration is shown below:
acceleration (a) = (Vf - Vi) / t
in this problem, we need to pick velocity final and initial such as:
Vf = 10 m/s
Vi = 8 m/s
Check the corresponding time, in this case, the time is (40seconds - 30seconds) equivalent to 10 seconds
Solving for the acceleration, we have it:
a = (10 - 8) / 10
a = 2/10
a = 0.2 m/s²

The answer is 0.2 m/s².

B, if it was a lower watt she could put it in for her normal time and not burn it