- #1
DiamondGeezer
- 126
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In one of my undergrad books on physics is the example of a rail truck of mass M on a frictionless railroad moving at a constant speed v, which is being filled with sand at a rate of x kg/s
If force F is applied to the truck, then the truck does not accelerate because
[tex]F=m \frac{dv}{dt} + v\frac{dm}{dt} [/tex]
Now as far as I can tell the truck continues at a constant speed unless [itex]F > v\frac{dm}{dt}[/itex]
(The book implies that the force must be applied to keep the velocity at v which is wrong)
What is the effect here? What happens if the truck is full of sand and there's a hole in the bottom which causes sand to leave at y kg/s ?
If force F is applied to the truck, then the truck does not accelerate because
[tex]F=m \frac{dv}{dt} + v\frac{dm}{dt} [/tex]
Now as far as I can tell the truck continues at a constant speed unless [itex]F > v\frac{dm}{dt}[/itex]
(The book implies that the force must be applied to keep the velocity at v which is wrong)
What is the effect here? What happens if the truck is full of sand and there's a hole in the bottom which causes sand to leave at y kg/s ?