A planet is moving around the sun in a circular orbit of radius R and with a time period T. If the planet is suddenly stopped in its orbit then (assume radius of sun is very small as compare to R)

It will fall onto the sun after a time $\frac{T}{4\sqrt{2}}$ .

The magnitude of mechanical energy after the stopping will become twice the initial magnitude of mechanical energy.

The mechanical energy will decrease.

Its angular momentum about the centre of the sun will become zero.