- #1
i_hate_math
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Homework Statement
A railroad car moves under a grain elevator at a constant speed of 4.50 m/s. Grain drops into the car at the rate of 420 kg/min. What is the magnitude of the force needed to keep the car moving at constant speed if friction is negligible?
Homework Equations
U=V+dV-Vrel , U is the velocity of dM, which is 0 in this case
dM/dt • Vrel = M • dV/dt where V is the velocity not volume
The Attempt at a Solution
So from the question, dM/dt is 420kg/min=70kg/s,
I played with the 1st rocket equation, was able to get (4.5+dV)*70=M*a=Force needed.
But how do I find dV with limited information on the system given?