1. a 700kg racecar slowed from 30m/s to 15 m/s. what was its change in momentum? 2. if the car in the above problem took 5 seconds to slow down from 30m/s to 15 m/s. a. what is the impulse? b. what was the average force applied by the brakes?

1. The change in momentum follows the formula:

Change in Momentum = mΔv,
where m is the mass and v is the velocity

Change in momentum = (700 kg)(15 m/s - 30 m/s) = -10,500 kg·m/s

2. For this problem, the formula for impulse, J, is

J = FΔt

Before answering part a, we answer for part b first.

Part B. 
F = ma
where
a = Δv/t = (15 - 30)/5 = -1 m/s²
So,
F = (700 kg)(-1 m/s²) = -700 N

Part A.
J = (-700 N)(5 s) = -3,500 N·s