Question

What is the average braking force required of a 1200kg car in order for it to come to rest from 60km/h in a distance of 25m
Physics - Damon, Monday, September 1, 2014 at 6:51am
Vi = 60 km/h (1 h/3600 s)(1000 m/km)

v = Vi + a t
0 = Vi + a t
t = -Vi/a

d = Vi t + (1/2) a t^2

25 = Vi (-Vi/a) + (1/2)a (-Vi/a)^2

25 = -Vi^2/a + (1/2)Vi^2/a
25 a = -(1/2)Vi^2

COULD YOU PLEASE PUT THE ANSWER THERE AS I DON'T GET IT

Answer 1

no
calculate Vi, the initial velocity, as I showed you.
then use Vi in the last line to get a, which is negative because we are braking.
Then
F = m a = 1200 a

Answer 2

I got an answer of -86400n but the answer is 6700n

Answer 3

Show me your steps.

Answer 4

I get -6667 N

Answer 5

You never converted km/hr to m/s
go back and do the first step I gave you

Vi = 60 km/h (1 h/3600 s)(1000 m/km)
and you will get initial velocity = 60/3.6

Answer 6

I found my mistake thanks

Answer 7

You are welcome.