What is the Kinetic Energy of a 3000lb Car Traveling at 60mph?

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Homework Help Overview

The discussion revolves around calculating the kinetic energy of a car, specifically a 3000lb vehicle traveling at 60mph. The problem involves understanding the distinction between pounds as units of force and mass, as well as the necessary conversions for velocity.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the conversion of pounds to kilograms and the implications of using pounds as units of mass versus force. There is discussion about the necessity of incorporating gravitational acceleration for accurate mass calculations.

Discussion Status

Some participants have provided insights into the conversion process and the relationship between force and mass. There is an ongoing examination of the assumptions regarding units, but no consensus has been reached on a definitive method for solving the problem.

Contextual Notes

There are mentions of missing data for calculations and the need to convert units from pounds to kilograms and from miles per hour to meters per second. The discussion reflects uncertainty about the correct interpretation of units in the context of kinetic energy calculations.

mbm
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Homework Statement



what is the kinetic energy of a 3000lb car traveling at a 60mph (pounds are not units of mass)

Homework Equations


KE=1/2* mass * velocity ^2


The Attempt at a Solution



pounds are the units of force but to calculate the mass I am missing some data unless I'm supposed to use gravity...
 
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You're confused because pounds are units of mass.
 
There is the the pound for force and the pound for mass.

1 pound of mass is about 0.454 Kilograms

1 pound of force is (0.454*g) Newton where g is the acceleration of gravity

Whether you take it to be pound of force or pound of mass you ll end up with the same result. (If you take it to be pound of force after you convert it to Newtons you ll have to divide by g to get the mass in kilograms)
 
mbm said:

Homework Statement



what is the kinetic energy of a 3000lb car traveling at a 60mph (pounds are not units of mass)

Homework Equations


KE=1/2* mass * velocity ^2


The Attempt at a Solution



pounds are the units of force but to calculate the mass I am missing some data unless I'm supposed to use gravity...

You have to convert 3000lbs to kilograms and 60 mph to meters per second (m/s)
 
thnx! I now understand!
 
alfredo24pr: I disagree. You are given W = 3000 lbs = mass of car * g
and V = 60 mph. m = 3000 / 32.2 lb-s^2/ft v = 60 * 5280 / 3600 ft/s

KE = (1/2) m*v^2 = (0.5) * (3000/32.2) *[60*5280/3600]^2
KE = 360,745 ft-lbs
 

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