Question

A cyclist is travelling at 15m|s-1. She applies brakes so that she could not collide with 18 m away what deceleration must she have

Answer 1

using formula v square equal to u square + 2as you can find a.

Answer 2

In this question we will calculate the negative acceleration/ decelaration, as follows:
Kinematic equations:
SUVAT-- s-displacement, u-initial velocity, v-final velocity, a-acceleration, t-time.
v=u+at v2=u2 + 2as=1/2(u+v)ts=ut+1/2at2
Her initial velocity, u is 15m/s
Her final velocity is, 0m/s(since she stops)
Displacement is, s 18m
Hence the acceleration, a:
v2=u2+2as
0=15^2 + 2 x a x 18
0=225+36a
36a=-225
a=-225/36
a=-6.25m/s/s
Therefore, she had to decelarate at the rate of 6.25m/s2