Forget about the car's speed. You don't need it.
The tires spin 840 rpm. That's 840 <em>Revolutions per Minute</em> .
There are 60 seconds in 1 minute. So something that happens 840 times in 1 minute happens (840 / 60) times every second.
(840 rev per minute) / (60) = <em>14 revs per second</em> .
Its a solar cell. Photo voltaic Cell is also known as a solar cell.
The answer would be it will be longer than the 656.3 nm. The reduced mass of positronium is less than hydrogen so the photon energy will be a reduced amount of for positronium than for hydrogen. So this will mean that the wavelength will be lengthier.
1.6 m/s west is the answer
