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chroot

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The definition of kinetic friction allows you to find the force experienced by the vehicle (you must assume it is independent of velocity).

Once you know the force, you can use Newton's second law to determine the acceleration -- it is constant.

Since the acceleration is constant, you can use the equation:

v(t) = v_{0} + a t

to calculate the time it took the car to stop (a is negative, of course), and the equation

s(t) = v_{0} t + 1/2 a t^{2}

to solve for v_{0}.

If these equations are new to you, let me know and I'll guide you through their derivation.

- Warren

Once you know the force, you can use Newton's second law to determine the acceleration -- it is constant.

Since the acceleration is constant, you can use the equation:

v(t) = v

to calculate the time it took the car to stop (a is negative, of course), and the equation

s(t) = v

to solve for v

If these equations are new to you, let me know and I'll guide you through their derivation.

- Warren

Last edited:

- #3

but all i have to start with is the 0,.330..how do i get the force from that?

- #4

chroot

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There's a simple equation relating two quantities: the friction force, and the normal force. The coefficient of (static or kinetic) friction is simply the proportionality constant between them. The equation is this one:

F = [mu]

= [mu]

Can you calculate F now?

- Warren

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chroot

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Sorry, I should be more specific. You don't need to actually compute a NUMBER for the force. You can leave it in symbolic form, like this:

F = [mu]

F = 0.33 m g

And just use it like that.

The next step is to calculate the acceleration experienced by the vehicle, which is given by Newton's second law:

F = m a

Plugging in your value for F yields this:

0.33 m g = m a

The m's cancel:

0.33 g = a

And you have the acceleration.

With me so far?

- Warren

- #6

yes, i understand that part..and then?

- #7

chroot

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Now that you have the acceleration, you can plug it into this equation:

v(t) = v

to find the time taken for the car to stop.

In other words,

0 = v

t = v

Now you can plug t into the equation

s(t) = v

And solve for v

- Warren

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