Question

The tip of a robot arm is moving to the right at 13m/s. Four seconds later, it is moving to the left at 2m/s. What is the magnitude of the change in velocity and what is the average acceleration? (Assume that the +x direction is the positive direction)

Answer 1

We know that velocity depends on time and acceleration as follows:

$$v(t)=v_0+at.\\ v(4)=-2=13+a\cdot4,\\ a=-3.75\text{ m/s}^2.$$

The magnitude of velocity change is

$$\Delta v=|v_f-v_i|=|-2-13|=15\text{ m/s}.$$