A car starts from rest and travels for 7.0 s with a uniform acceleration of +3.0 m/s2. The driver then applies the brakes, causing a uniform acceleration of −2.5 m/s2. If the brakes are applied for 2.0 s, determine each of the following.

Question

(a) How fast is the car going at the end of the braking period?
I know the answer for this one is 16 m/s

(b) How far has the car gone?

How do you do this one?

Answer 1

The same way as the last one. At least you do not have centimeters
first phase, acceleration
u1 = 0 + a t1
x1 = 0 + 0 t1 + .5 a1 t1^2
second phase braking
u2 = u1 - 2.5(2)
x2 = x1 + u1(2) - .5 (2.5)(2)^2