Physics Question: How to find acceleration and total distance

Question

A car stopped at a red light starts moving when the light turns green and accelerates

at the rate of 2.7 m/s2 for 15 seconds. The driver continues at this speed for 10

seconds until he sees the next traffic signal turning red 191 m away. He reacts after 2

seconds and slams on his brakes.

1)What is the car’s acceleration if he stops just as he reaches the light?

2)What is the total distance covered by the car?

Answer 1

Well his speed after the initial acceleration is 2.7 x 15 = 40.5 m/s

He stops at the red 191 m away

v² = u² + 2as

v = 0 (as he stops)

u = 40.5 m/s

s = 191 m

You can calculate a now (it will be negative as he brakes)

Total distance ...

Until the point that he brakes.

First 15 seconds. s = ut + 0.5at² . u = 0, t = 15, a = 2.7. Find s.

Next 10 seconds s = ut + 0.5at² u = 40.5, t = 10. a = 0 (constant speed). Find s

Add these two distances together, then add 191 to find total distance.