A140-lb man carries a 25-lb can of paint up a helical staircase that encircles a silo with radius 30 ft. if the silo is 120 ft high and the man makes exactly three complete revolutions, how much work is done by the man against gravity in climbing to the top?

633600 lb-ft.

Explanation:

In a conservative field , work done does not depend upon the path followed. It depends only on the initial and final point . Here work done as asked in the question will be equal to lifting the object straight to height of 120 Ft

So work done

= mgh

= ( 140 + 25 ) x 32 x 120

= 633600 lb-ft.

second mirror gathers light from a faraway object and reflects it to another mirror. - a.

hypothesising or postulating