You have a beach ball which has a radius of 22 cm and a mass of 0.2 kg. You have

ID: 250681 • Letter: Y

Question

You have a beach ball which has a radius of 22 cm and a mass of 0.2 kg. You have a lead ball which has the same radius but has a mass of 120 kg.

Part A -You immerse the beach ball under the water. What is the buoyancy force felt by the beach ball?

Part B -To keep the beach ball stationary under the water what is the force you need to apply? (UP is positive)

Part C -You immerse the lead ball under the water, what is the buoyancy force felt by the lead ball?

Part D -To keep the lead ball stationary under the water what is the force you need to apply? (UP is positive)

Buoyacy force = V*rho*g

V = 4/3*pi*(r)^3

(A) Buoyacy force on beach ball = 4/3*pi*(r)^3 * 1 * 9.8

Fb = 4/3 * 3.14 * (22 x 10^-2)^3 * 9.8

Fb = .43 N

(B) Gravity on beach ball = mg = .2 x 9.8 = 1.96 N

Fb = .43 N

net force = 1.96 - .43 = 1.53 N (on upward side to keep the ball stationary)

Fb = 4/3 * 3.14 * (22 x 10^-2)^3 * 1 * 9.8

Fb = .43 N (same as beach ball)

(D) gravity on lead ball = mg = 120 * 9.8 = 1176 N

Fb = .43 N

Net force to keep the ball stationary = 1176 - .43 = 1175.57 N (on upward side)

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