What is the speed of a wave if the wavelength is 100m and the period is 20s

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?

Yvette hangs a 2.4kg bird feeder in the middle of a rope tied between two trees. the feeder creates a tension of 480 n in each side of the the rope.

If the radius of curvature of the cornea is 0.75 cm when the eye is focusing on an object 36.0 cm from the cornea vertex and the indexes of refraction are as described before, what is the distance from the cornea vertex to the retina? express your answer to two significant