Friction: decelerating vehicle on dry and wet concrete

AI Thread Summary
The discussion revolves around calculating the stopping distance and time for a pickup truck braking on dry and wet concrete. Key concepts include the use of the coefficient of kinetic friction (μk) to determine acceleration, with the relationship a = -μk * g being emphasized. Participants suggest using free-body diagrams and velocity-time graphs to visualize the problem and understand the forces involved. The importance of understanding the fundamentals of physics and not just plugging in numbers is highlighted. Overall, the conversation focuses on guiding the original poster to apply physics principles to solve the problem effectively.
tratata
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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
 
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hi tratata! :smile:

from µ, you can find the acceleration

does that help? :wink:
 
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?
 
Tiny-tim, but how? ;)) a little more help please or direction to go! I've been struggling with this one half the night
 
What is the relationship between friction force, ##\mu_k## and acceleration?
Hint: Newton's laws.

This is why you want the fbd.
 
tratata said:
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 … ? :smile:
 
Simon: a=μk*g? ;)
 
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?
 
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