Register to reply

Elementary Physics help.

by jtm
Tags: elementary, physics
Share this thread:
jtm
#1
Oct17-05, 12:19 AM
P: 19
This problem I have to do is really bothering me.

Your 1600 kg PT Cruiser moves around a level 50m radius road. The coefficient of STATIC friction between the car tires and the road is 0.80. Determine the MAX speed of the car so that it does not skid off the road.


I think I get somewhere around.

ma - mg*0.80 = mv^2 / R I'm sure this is wrong because m shouldn't be able to be cancelled. Always ALL the information provided is used in the calculation.
Phys.Org News Partner Science news on Phys.org
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'
Tide
#2
Oct17-05, 12:36 AM
Sci Advisor
HW Helper
P: 3,144
jtm,

m shouldn't be able to be cancelled.
Why not?
jtm
#3
Oct17-05, 01:04 AM
P: 19
Always ALL the information provided is used in the calculation.

Also, it gives the wrong answer ;) I checked.

Gokul43201
#4
Oct17-05, 01:20 AM
Emeritus
Sci Advisor
PF Gold
Gokul43201's Avatar
P: 11,155
Elementary Physics help.

Quote Quote by jtm
This problem I have to do is really bothering me.
Your 1600 kg PT Cruiser moves around a level 50m radius road. The coefficient of STATIC friction between the car tires and the road is 0.80. Determine the MAX speed of the car so that it does not skid off the road.
I think I get somewhere around.
ma - mg*0.80 = mv^2 / R I'm sure this is wrong because m shouldn't be able to be cancelled. Always ALL the information provided is used in the calculation.
1. What is 'a' ?
2. The answer is independent of the mass, m.
jtm
#5
Oct17-05, 01:22 AM
P: 19
Answer from what I have on key is 6.3 m/s I am getting 19.8 m/s with mass cancelling out. We don't have a :) I'm assuming 0.
Diane_
#6
Oct17-05, 01:40 AM
HW Helper
P: 397
Think about this one physically first. If the car is going in a curve, there must be a centripetal force acting. Where is that force coming from? What you're looking for is the speed at which the maximum value of the force providing the centripetal force is exactly what's necessary to hold the car on the road. If it goes any faster, that force will not be able to hold it, and the car will skid.

So - at the point in which you're interested, the centripetal force must equal the maximum of the force providing it. You'll find the masses do cancel out. Sometimes teachers will give you information you don't need, to see if you'll find a way to stick it in anyway. I speak from experience.
Gokul43201
#7
Oct17-05, 11:57 AM
Emeritus
Sci Advisor
PF Gold
Gokul43201's Avatar
P: 11,155
Quote Quote by jtm
Answer from what I have on key is 6.3 m/s I am getting 19.8 m/s with mass cancelling out. We don't have a :) I'm assuming 0.
19.8 m/s is correct. The key is wrong. They forgot to multiply by 'g' !

PS : Did you draw a free-body diagram ?


Register to reply

Related Discussions
Elementary Quantum Physics Biology, Chemistry & Other Homework 0
Elementary physics or not? Introductory Physics Homework 29
Elementary physics in 1 dimension Introductory Physics Homework 2
A couple of elementary physics questions Introductory Physics Homework 13
An Elementary question for general physics Introductory Physics Homework 1