How Do You Calculate Car Mass from Kinetic Energy Change?

AI Thread Summary
To calculate the mass of a car from the change in kinetic energy, the correct formula is Change in Kinetic Energy = 0.5mv2^2 - 0.5mv1^2. Given the initial speed of 18 m/s, final speed of 35 m/s, and a change in kinetic energy of 154 kJ, the mass can be derived from this equation. The discussion clarifies that the equation for kinetic energy is essential for solving the problem, and the correct approach involves using the change in kinetic energy to find the mass. Participants confirm that the inclusion of the 1/2 factor is crucial in the kinetic energy formula. The conversation emphasizes understanding the relationship between kinetic energy and mass for accurate calculations.
Marts12
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Homework Statement



A) A car moving at 18 m/s is accelerated to 35 m/s. If the change in kinetic energy is 154 kJ, determine the mass of the car.

Homework Equations



KE = 0.5mv^2
Kinetic energy = change in momentum = mv2-mv1


The Attempt at a Solution



Im not sure how to go about this problem, but I suspect that the mass can be obtained from the fact that kinetic energy is equal to the change in momentum?
 
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Marts12 said:
KE = 0.5mv^2
Kinetic energy = change in momentum = mv2-mv1

Aren't these two equations contradictory? Which one is correct?
 
KE=0.5mv^2 is the correct equation for kinetic energy, but we are given that.

Am I right in saying that I need an equation that relates the change in Kinetic energy to mass?
 
Marts12 said:
KE=0.5mv^2 is the correct equation for kinetic energy, but we are given that.

Am I right in saying that I need an equation that relates the change in Kinetic energy to mass?
Yes, and you already have all the ingredients to construct that equation yourself.
 
Ok,

If I were to say that Change in Kinetic Energy = mv2^2 - mv1^2

Where v2 = final velocity and
V1 = initial velocity

Would I be on the right lines?
 
Marts12 said:
Ok,

If I were to say that Change in Kinetic Energy = mv2^2 - mv1^2

Where v2 = final velocity and
V1 = initial velocity

Would I be on the right lines?
Nearly, but you lost the 1/2.
 
Perfect so,

Change in Kinetic Energy = 0.5mv2^2 - 0.5mv1^2

Thank you for your help DrClaude
 
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