Question

A cyclist is travelling at 15 m s-1. She applies brakes so that she does not collide with a wall 18 m away.
What deceleration must she have ?
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Answer 1

Answer:

given : u = 15 m/sec, v = 0, s = 18 m

to find : deceleration

formula : v² - u² = 2as

=> 0² - 15²0 = 2×a×18

=> -225 = 36 a

=> a = -225/36

=> a = - 6.25 m/sec²

=> deceleration = - 6.25 m/sec²

Answer 2

Step-by-step explanation:

In this question we will calculate the negative acceleration/deceleration, as follows:

Kinematic equations:

SUVAT-- s-displacement, u-initial velocity, v-final velocity,a- acceleration, t-timev=u + atv2 = u2 + 2ass=1/2(u+v)ts=ut + 1/2at2

Her initial velocity, u is 15m/s

Her final velocity is, v 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= -6.25 m/s/s

Therefore she has to decelerate at the rate of 6.25m/s2