The problem is in the picture. we know the alpha angle and the constant value of velocity v. then find the value of speed "u" when the thread makes angle alpha with horizontal.

u = v / cos α

Explanation:

Sorry for my first try. I think I figured it out this time.

When you pull on the rope the block wants to go in the direction v. But it has to stay on the plane. So it will also move in the direction w. (see my picture) The result is that the block moved in the direction u, which is the vectorial sum of v and w.

All three vectors form a right triangle, where v = u * cos α. If you solve for u, you will get: u = v / cos α

Neptune is the eighth planet from the sun. it was the first planet to get its existence predicted by  mathematical calculations  before it was actually seen through a telescope on sept. 23, 1846. irregularities in the orbit of  uranus  led french astronomer alexis bouvard to suggest that the gravitational pull from another celestial body might be responsible. german astronomer johann galle then relied on subsequent calculations to   spot neptune via telescope. previously, astronomer galileo galilei sketched the planet, but he mistook it for a star due to its slow motion. in accordance with all the other planets seen in the sky, this new world was given a name from greek and roman mythology — neptune, the roman god of the sea.