Car collision problem. Conservation of momentum

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Homework Help Overview

The discussion revolves around a car collision problem involving conservation of momentum and mechanical energy loss. The scenario includes a car and a truck moving in the same direction, with specific masses and initial velocities provided.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the mechanical energy lost in the collision by subtracting the kinetic energies of the car and truck. Some participants question the completeness of this approach, noting the need to consider the truck's velocity after the collision.

Discussion Status

Participants are actively engaging with the problem, with some providing guidance on the application of conservation of momentum. There is an acknowledgment of the need for the original poster to clarify their understanding and approach to the problem.

Contextual Notes

The original poster is new to the forum and is navigating the rules regarding posting attempts before receiving help. There is an indication of a misunderstanding regarding the conservation laws applicable to the scenario.

physicgeek
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A 1100 kg car traveling initially with a speed of 25.0 m/s in an easterly direction crashes into the rear end of a 8200 kg truck moving in the same direction at 20.0 m/s . The velocity of the car right after the collision is 18.0 m/s to the east.

1.How much mechanical energy is lost in the collision?



Thank you
 
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Hello physicgeek, you need to post your attempt at the problem before anyone at PF can help you as per the rules.
 
rock.freak667 said:
Hello physicgeek, you need to post your attempt at the problem before anyone at PF can help you as per the rules.

sorry I am new.

what i did was i took the kinetic energy of both and subtracted them.
but i got it wrong on webassign. (online homework)
 
physicgeek said:
sorry I am new.

what i did was i took the kinetic energy of both and subtracted them.
but i got it wrong on webassign. (online homework)

ah, I see. You forgot that that after the collision, the truck is still moving.

How would you go about finding the velocity of the truck? What law would you apply?

(Hint: it's in your thread title)

When you get that, find it for before the collision and after the collision and equate them.
 

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