A student lifts a 90 pound (lb) ball 4 feet (ft) in 5 seconds (s). How many joules of work has the student completed?

A) 770J

B) 369J

C) 488 ft lbs

D) 488.6 J

Wending your way through this question and the list of choices

is like running through a corn-maze on a moonless night with

your eyes closed.

Work = (force) x (distance)

Keeping with the units used In the question ...

Work = (90 pounds) x (4 feet) = 360 foot-pounds.

If you want the work expressed in joules, then you need to convert

pounds and feet to newtons and meters.

(90 pounds) x (4.448 newtons/pound) = 400.32 Newtons

(4 feet) x (1 meter / 3.28084 feet) = 1.219 meters

Work = (force) x (distance)

= (400.32 newtons) x (1.219 meters) = 488.1 joules.