Newton's Laws?

Question

The driver of a truck slams on his brakes and skids to a stp through a distance d.
If the truck carried a diff load that its mass were quadrupled, what would be the skidding distance?
____*d

Answer 1

Friction force stops the truck when the brakes are applied. Friction force F = kN; where k is the coefficient of friction and N is the normal weight of the truck.

F = ma= kN = kmg ; so that a = kg where g = 9.81 m/sec^2 or 32.2 ft/sec^2 on Earth's surface. The stopping distance d = 1/2 at^2; so that d = 1/2 kgt^2. And, lo, what do we see? m, the mass of the truck, has disappeared. k and g are constants. What about t, the time to stop?

From v = u - at = 0; we have u = at and t = u/a = u/(kg); where u is the initial velocity when the brakes are applied. Thus we have d = 1/2 kgt^2 = 1/2 kg(u/kg)^2 = u^2/2kg. And look at this....

d does not depend on m the mass of the truck at all. The only thing it does depend on in reality is the coefficient of friction, which means wetter slippier roads will give lower k and higher d; and on the initial velocity u when the brakes are applied. So the answer, in brief, with a quadruple load, the truck will still stop in distance d if the road conditions are the same and the starting velocity is the same.

Answer 2

i had this same question in my homework a week or so ago.
wow
and no, i dont remember