## Posts Tagged ‘seconds.’

### a model electric train makes one complete pass around a circular track every 15 seconds….?

Wednesday, October 31st, 2012

Question by moniquew93: a model electric train makes one complete pass around a circular track every 15 seconds….?
a model electric train makes one complete pass around a circular track every 15 seconds. the train’s motor has a resistance of 6.0ohm and is connected to a 70.0V source. How much energy will the train use in 12 complete passes around the track?

This question cannot be answered. Model-train motors don’t draw the huge wattage implied by the voltage and resistance, which = V^2/R = 816.67 W. At running speed the motor would generate a back EMF which would substantially reduce the actual voltage across the internal resistance. See the ref.
EDIT: The input data are not necessarily crazy, just incomplete. What’s crazy is the assumption that the given V is applied across the given R continuously; it actually would only happen momentarily at startup.

What do you think? Answer below!

### A 150 m long train crosses an electric pole in 10 seconds. Calculate the speed of the train?

Monday, August 6th, 2012

Question by : A 150 m long train crosses an electric pole in 10 seconds. Calculate the speed of the train?
A 150 m long train crosses an electric pole in 10 seconds. Calculate the speed of the train? 