Question

A car was moving with the velocity of 108 km/h and the driver saw the red signal 100 m away and he applied the brakes to stop the car in 5 s. How many meters before the traffic signal will he be able to stop?

Answer 1

Answer: Your answer is 43.8m Explanation: Here v=108km/h=30m/s S=100. T=5sec  FROM EQUATION OF MOTION S=ut+$\frac{1}{2}$at² 100=0*t+

Answer 2

u = 108 km/h = (108000/3600 )m/s = 30 m/s

v = 0 m/s [since car had stopped finally ] ; t= 5s

now, a = (v-u)/t = {(0-30)/5}m/s^-2 = -6 m/s^-2

[here we get that acc is negative... which means there is retardation taking place.... in physics - sign not always says that the value is negative and u r wrong.. ]

now,

s = ut + 1/2 at^2 => s = [30(5) + 1/2.-6(5)^2 ] m

=> s = (150 - 75 )m => s = 75m

therefore we can say that the car stopped at 75m which is 25 m far frm the signal.....

here a is acceleration , t is time , v is final velocity , u is initial velocity, s is displacement. .

since here there is no Δdirection.. dist. = s..

hope it helps..