Friction: decelerating vehicle on dry and wet concrete

[tratata]

Homework Statement

A pick up truck is traveling at 58 km/h on a dry horizontal concrete surface when the driver applies the brakes locking the wheels. (a) How far does the car travel before coming to rest? (b) How long does it take the car to stop after the driver applies the brakes? (c) How far does the car travel before coming to rest if the concrete surface is wet?

Homework Equations

The Attempt at a Solution

I can't even understand where to start! Please offer any suggestions. I can't find any equation where just the velocity would be sufficient. I have V1 and V0 but absolutely nothing else - well also μk and μs. ok wait if I have μs that should somehow help me...but how? Any help greatly appreciated! Kind regards,
Kate

 

[tiny-tim]

hi tratata!

from µ, you can find the acceleration

does that help? ​

 

[Simon Bridge]

Don't try to find an equation to plug numbers into to get the answer. Instead, use your understanding of physics to write an equation.

Can you sketch a v-t diagram of the motion?
Can you draw a free-body diagram for the forces on the car?
Do you know the coefficient of kinetic friction for the surfaces involved?

 

[tratata]

Tiny-tim, but how? ;)) a little more help please or direction to go! I've been struggling with this one half the night

 

[Simon Bridge]

What is the relationship between friction force, $\mu_k$ and acceleration?
Hint: Newton's laws.

This is why you want the fbd.

 

[tiny-tim]

Tiny-tim, but how? ;)) a little more help please or direction to go! I've been struggling with this one half the night

exam questions usually tell you everything you need to know

if you can't see what the answer is, go back to fundamentals and ask yourself what everything in the question means

in this case, what is meant by the coefficient of friction?

it's the … ? ​

 

[tratata]

Simon: a=μk*g? ;)

 

[Simon Bridge]

acceleration is a vector :)
if the pickup starts out moving in the +x direction, then $a=-\mu_k g$.
but you should not just present someone with your end result - show your reasoning.

Would the deceleration be constant or would it change?
Can you sketch a velocity-time graph of the motion?