Asked by abhishek
A car is travelling at 20m/s along a road. A child runs out into the road 50m ahead and the
car driver steps on the brakes pedal. What must the car’s deceleration if the car is to stop just
before it reaches the child?
car driver steps on the brakes pedal. What must the car’s deceleration if the car is to stop just
before it reaches the child?
Answers
Answered by
Steve
at deceleration a, the velocity is
v = 20-at
so t = 20/a
the distance traveled by the car is
s = 20t + 1/2 at^2
= 20(20/a) - 1/2 a (20/a)^2
= 200/a
So, to stop in 50 meters,
200/a = 50
a = 4 m/s^2
check:
v = 20-4*5
s = 20*5 - 2*5^2 = 100-50 = 50
v = 20-at
so t = 20/a
the distance traveled by the car is
s = 20t + 1/2 at^2
= 20(20/a) - 1/2 a (20/a)^2
= 200/a
So, to stop in 50 meters,
200/a = 50
a = 4 m/s^2
check:
v = 20-4*5
s = 20*5 - 2*5^2 = 100-50 = 50
Answered by
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