Minecart that has stopped on a non-powered Powered Rail won't start moving when power is applied.

I built a railway where a chest cart stops on a non-powered powered rail under a hopper, and when the hopper is empty a redstone current is applied to the powered rail to make the cart move forward.
It stops under the hopper but when the redstone signal is applied it doesn't move.

I have tried this without the hopper and applying the redstone with a lever, but it still won't make the cart start moving again.