Locomotive throwing sand in a car

Thread starter Saitama
Start date Aug 22, 2013
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Car Locomotive

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SUMMARY

The discussion centers on a physics problem involving a sand-spraying locomotive and a freight car. The locomotive sprays sand at a rate of 10 kg/s with a velocity of 5 m/s, while the freight car, starting from rest with an initial mass of 2000 kg, maintains a constant distance from the locomotive. Participants analyze the momentum conservation principles and variable-mass systems to derive the car's speed after 100 seconds, ultimately leading to the differential equation for the car's velocity.

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Understanding of momentum conservation principles
Familiarity with variable-mass systems
Basic knowledge of differential equations
Concept of inertial and non-inertial reference frames

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Physics students, educators, and professionals interested in mechanics, particularly those focusing on variable-mass systems and momentum conservation principles.

Aug 23, 2013

Saitama

ehild said:

If you use the car as system of reference, you can not speak about the change of its velocity. In its own frame of reference,the velocity is identically zero.
It has no sense choosing a system as frame of reference, the motion of which you do not know. You want to find the velocity of the car with respect to the ground as function of time.

As voko said, choosing the car as frame of reference means a non-inertial frame. In that frame, the virtual force -ma acts on every mass m, and the equation you got from conservation of momentum is not valid.

Thanks ehild and voko! This was an interesting thread. :)