A 1500kg car skids to a halt on a wet road where μk= 0.53. How fast was the car traveling if it leaves 62-m-long skid marks?

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asked by Angela

Oct 28, 2009

First draw a free-body-diagram with Fn (normal force) pointing upward mg(Fg) pointing downward and the force of friction Ff to the left. Then set your axis for this problem I choice up and to the left as positive.

So you use Newtons 2nd law to find Fn

So the summation of Fy=ma

Since there is no motion in the y direction a=0

So it is Fg-ma so it’s Fg=ma and it’s (1500)(10) which gives you 15000N

Then you find Ff

Ff=u(mew)Fn

Ff=(.5)(15000)

Ff=7500N

Then you use F=ma because you are trying to find acceleration in the x direction which means you have to use the Ff because it is in the x direction so you get :

A=Ff/m

A=5 m/s^2

Then you need to find the initial velocity Vi so use

Vf^2=Vi^2 + 2ad

Vf=0 because it skids to rest so

0=Vi^2 + 2ad

-2ad=Vi^2

When you work all of it out you get -25.5 m/s it something around there

Hope this helped

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posted by Phanor

Oct 7, 2014