Say there is a 10N pendulum held parallel to the ground. In a frictionless environment, it will continue swinging along a semicircular path. The pendulum tip should have the highest horizontal component of velocity at the very bottom $[ 90^o ]$, and lowest at the top $[ 0^o ]$ , $[ 180^o ]$.
What can similarly be said about the vertical component of velocity? At what angle during its swing will the tip be traveling fastest downwards and fastest upwards?
At the top of the swing, all of the pendulum's velocity is in the vertical direction, but the total velocity is zero. At the bottom of the swing, there is no up/down component of motion, and vertical velocity is again zero. $[ 45^o ]$ and $[ 135^o ]$ seem reasonable, as they're halfway between.