Question

A motorcyclist A , riding motorcycle travelling at 40km/h,applies brakes and stops the motorcycle in 10s and another motorcyclist B , travelling at 20km/h , applies the brakes and stop the motorcycle in 20s.Plot the time graphs for the two motorcycles.​

Answer 1

Case I:
For motorist A,
Initial Velocity= u=36km/h=36x5/18=10 m/s
Time=t=10s
by using third equation of motion:
V²-u²=2as
0-10x10=2s(V-u)/t
0-10x10=2s(0-10)/10
-2s=-100s
=100/2=50m
Case II:
For motorist B,
Initial velocity=18km/h=18x5/18=5m/s
time=t=20s
By using third equation of motion:
V²-u²=2as
V²-u²=2s(v-u)/t
0-5x5=2s(0-5)/20-25=-s/2s=50m
so both  A and B cover the same distance.
To draw graph ;we need to find acceleration:
For Motorist A:a=(v-u)/t=(0-10)/10=-1 m/s²
For Motorist B:a=(v-u)/t=(0-5)/20=-0.25 m/s²
Time is from 0 to 20 sec and speed is from 5 to 0.25 m/s
Please refer the attachment for the graphs:
Graph 1- Motorist A
Graph 2- Motorist B