Question

A girl turns over a plastic cup so that the open end is facing down, and thencompletely submerges it in a pool of water. In doing so, she traps air in thecup so that both the air and the cup have a volume of 237 cmApproximately how much force must she use to keep the cup from poppingup out of the water, assuming that the weight of the cup and air can beneglected? (Recall that the density of water is 0.001 kg/cm and g = 9.81m/s2.)O A. 7.5NB. 2.3 NO C. 11.6 NO D. 4.6 N

Answer 1

The buoyant force is equal to the weight of the water displaced.

Volume: V = 474 cm^3 = 0.000474 m^3

Density of water: ρ = 0.001 kg/cm^3 = 1000 kg/m^3

Specific weight is the weight of a unit volume of something, usually the weight of a cubic meter or a cubic foot.

Specific weight: γ

γ = ρ*g = 1000 kg/m^3 * 9.81 m/s^2 = 9810 N/m^3

W = γV = 9810 N/m^3 * 0.000474 m^3 = 4.64994 N

Closest answer would be D: 4.6 N