Physics problem? Please explain first class ?

Question

A motorist is traveling at 20m/s . he is 60 m from the spotlight when he sees it turn 0. his reaction time before stepping on the break is 0.5 s. what steady deceleration while breaking will bring him to a stop, right at light?

Answer 1

...is this a math question from your homework?

Answer 2

A basic equation of motion is:

v² = u² +2ad

Where:

v = final velocity

u = initial velocity

a = acceleration rate

d = distance traveled

solving for a:

a = (v² - u²)/2d

The car traveled 20 m/s * .5 s = 10 m before braking, so

d = 50

Since the final velocity is 0:

a  = - (20m/s)² / 2*50 m

a = - 400 m²s²/100 m

a = - 4 m/s²

The "-" sign means deceleration.