A projectile is launched at a speed of 141m/s and an angle of 45 degrees. How fast is it moving at the top of its curved trajectory?

Answer 1

Since the object is at the top of its trajectory its change in altitude (sin velocity) should be 0.
Then you just need to calculate for the speed in the horizontal axis(which never changes in simple projectile motion).

It becomes 141 cos(pi/4)
or 141 cos (45) if you prefer degrees.

This is of course assuming that its a simple projectile motion.