## Conceptual Physics (12th Edition)

a. Start with the equation at the top of page 42. $$L = v_{average}\times time$$ However, from the discussion on page 48, we know that the average speed under constant acceleration is the average of the initial and final velocities. $$v_{average}=\frac{0+v}{2}=\frac{v}{2}$$ Combine the above equations. $$time = \frac{L}{v_{average}}=\frac{L}{v/2}=\frac{2L}{v}$$ b. Plug in numbers. $$time =\frac{2L}{v}=\frac{2\times1.4m}{15.0m/s}=0.19s$$