Question

The driver of a car moving with a speed of 10 ms^-1 sees a red light ahead, applies brakes and stops after covering 10 metre distance. If the same car were moving with a speed of 20 ms^-1, then the same driver would have stopped the car after covering 30 m distance. Within what distance the car can be stopped if travelling with a velocity of 15 ms^-1? Assume the same reaction time and the same deceleration in each case

Answer 1

v = 0m/s
u = 20m/s
s = 10m
2as = v² - u²
2×a×30 = -400
a = -400/60 = -100/15 m/s

.........

now,
v = 0m/s
u = 15m/s
a = - 20m/s

2as = v² - u²
2×-100/15×s = -225
s = 225/200/15 = 16.875m

Answer 2

Answer:

22.5 ms

Explanation:

u=10ms

s=10m

v=0ms

v2-u2=2as

0-100=2a10

a=-5ms^-2

therefore

u=15m/s

s=?

v=0

similarly

0-225=2(-5)s

s=22.5