A driver of a car going 40 m/s (approx. 90 mph) suddenly sees the lights of a barrier 40.0 m ahead. It takes the driver 0.75 s before he applies the brakes (this is known as reaction time). Once he does begin to break the decelerates at a rate of 10.0 m/s^2 (Be careful of signs). Does he hit the barrier?

Explanation:

Distance of barrier = 40 m

Distance covered during reaction time = .75 x 40 = 30 m .

distance covered during deceleration can be calculated as follows .

v² = u² - 2 a s

0 = 40² - 2 x 10 x s

s = 80 m

Total distance covered before coming to rest = 30 + 80 = 110 m

Distance of barrier = 40 m , so it will hit the barrier .

the average speed is 24.57 km/hr

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