Assume you are driving a car at a constant speed of 78.0 km/h. Suddenly you see

Question

Assume you are driving a car at a constant speed of 78.0 km/h. Suddenly you see a deer standing on the highway and you must put on the brakes. Your reaction time (time elapsed between the moment you see the deer and your foot hitting the brakes) is 0.130 sec. The brakes provide an acceleration with a magnitude of 4.6 m/s2, and a direction opposite the initial velocity.

A) Find the distance (in m) the car travels (at 78.0 km/h) during your reaction time.

B) Calculate the total distance (in m) traveled by the car before stopping.

Explanation / Answer

Solution:

78km/hr Speed in m/sec= 78* (5/18)= 21.67 m/sec

Now, Distance travelled by car during our reaction time= 21.67 m/sec* 0.130 sec=2.82m (i) Ans.

Distance travelled during deceleration is calculated using

v2=u2+2as

0=21.672 + 2* (-4.62)* s

s=50.82 m

Total distance= 2.82 + 50.82= 53.64 m (ii) Ans.

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