f.4 phys,,mechanics,,about car.

a. Consider the journey when decelerating.

Initial speed, u = 18 ms-1

Final speed, v = 0

Acceleration, a = -6 ms-2


By v2 = u2 + 2as

0 = (18)2 + 2(-6)s

Braking distance, s = 27 m

Now, during reaction time, the car is moving with uniform velocity.

By d = ut

d = (18)(0.6) = 10.8 m

So, total stopping distance = d + s = 10.8 + 27 = 37.8 m

which is smaller than the initial distance between the car and the dog.

So, the car will stop before it hits the dog. Therefore, it will not hit the dog.


b. Now, thinking distance, d = 1.2(18) = 21.6 m

Total stopping distance = d + s = 21.6 + 27 = 48.6 m

which is larger than the initial distance between the dog and the car.

So, the car will hit the dog.

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