How much distance does it take to stop a car going 30 m/s (67 mph) if the brakes can apply a force equal to one half the car’s weight?

Question

abhisar · Answer

Hey there!
Welcome to OpenStudy :-)

Is mass of car given?

karabella98 · Answer

Hello! No, the mass is not given.

abhisar · Answer

It's ok. We can still solve it :-)

abhisar · Answer

So, let's see what are we given,

Initial speed (u) = 30 m/s
Since we want to stop the car, final velocity (v) will be 0

Also the maximum breaking force can be half of the car's weight, if we assume m as the car's mass then it would be mg/2. This means retardation of the car will be g/2$\approx$5

Now we have to calculate the distance. We can do this by using the formula

$\sf v^2=u^2-2as$

karabella98 · Answer

I got d=900m. Is that right?

abhisar · Answer

How are you getting that?

Calculate s using the formula I gave you...

abhisar · Answer

$\sf 0^2=(30)^2-2\times 5 \times s$, find s. That would be the answer

karabella98 · Answer

89m

abhisar · Answer

Yep, 90 m