A 2000kg car experiences a braking force of 10000N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was

A) 45 m/s

B) 15 m/s

C) 1.2 m/s

D) 30 m/s

E) none of these

So far I got a = 5m/s^2 and u = 30m/s but I think the answer is 45 m/s but I do not know where to go from there.

D. 30m/s

Explanation:

According to the equation of motion

v=u + at

v = Final velocity

u = initial velocity

a = acceleration

t = time taken

Since we don't know the acceleration of the body, we will find its acceleration using newtons first law of motion F = ma

10000 = 2000a

a = 5m/s²

initial velocity = 0m/s since the body starts from rest

v is what we are looking for

t = 6seconds

Substituting this datas in the formula

v = 0 + 5 (6)

v = 30m/s (D)