This is like the related rates ladder problems.
Use Pythagoras to find y given x=5/2 and the hypoteneuse of the triangle is 5, then you have all the info to find dx/dt
A construction worker at the top of a building is pulling, with a rope, one end of a five-meter plank up a buildings vertical side. The non-rope end of the plank rests on the ground. Therefore the buildings side, plank, and ground form a right triangle. If the rope end of the plank is being pulled up at a rate of 0.15 m/sec. How fast (rate of change) is the other end of the plank moving toward the base of the building when the end of the non-rope end is 2.5 meters from the building?
Last problem on my HW sheet and it's really giving me trouble
Any help would be really great