Why might a pump be needed in hydraulic system?

An object weighs 40n in air, weighs 20n when submerged in water and 30n when submerged in a liquid of unknown density. what is the density of the liquid?

Suppose you have a box. which of these is not necessarily a true statement regarding the relationship between the force applied to the box, the work done on the box, and the distance the box is moved? a. if the box is not moved, no force is being applied to the box. b. if no force is applied to the box, no work is done on the box. c. if work is done on the box, then a force is applied to the box. d. if work is done on the box, then the box is moved a distance.

Sound is a disturbance that travels through a medium as a