Worksheet on Buoyant Force

Worksheet on Buoyant Force
1- A 13-newton object is placed in a container of fluid. If the fluid exerts a 60-newton buoyant (upward)
force on the object, will the object float or sink?
Buoyant force (Upward) is higher than the Weight (downward) , so the object will float
2- The rock weighs 2.25 Newtons when suspended in air. In water, it appears to weigh only 1.8 Newtons.
Why?
Answer: The water is exerts a buoyant force on the rock. This buoyant
force equals the difference between the rock’s weight in air and its
apparent weight in water.
The water exerts a buoyant force of 0.45 N on the rock. 3- A 4.5-newton object is placed in a tank of water. If the water exerts a force of 4.0 Newtons on the
object, will the object sink or float?
Buoyant force= 4 N (Upward) is less than the Weight (4.5 N, downward) , so the object will Sink
4-‐ The same 4.5-newton object is placed in a tank of glycerin. If the glycerin exerts a force of 5.0 N on the
object, will the object sink or float? Buoyant force= 5.0 N (Upward) is higher than the Weight (4.5 N, downward) , so the object will Float
5-‐ Complete sentences. Show all work. a. The force that makes an object float is called the ____Buoyant Force__________________________. b. When the force of gravity is stronger than the buoyant force, an object will SINK/FLOAT. c. When the buoyant force is stronger than the force of gravity, an object will SINK/FLOAT. d. When the buoyant force is equal to the force of gravity an object will suspend/Float… e. A substance will float on top of water because: When the density of an object is higher than water density it will sink, but when its density is less that water density it will float 6-‐ Find the pressure of a 5 kg box exerts on the floor if it has a length of 0.25 m, a width of 0.20 m. Pressure=F/A F= mass X G = 5 X 9.8= 49 N A= 0.25 X 0.2 = 0.05 m2 So pressure= 49/ 0.05= 980 Pascal 7-‐ A box hat is 2 meters long, 60 cm wide and 40 cm tall exerts a pressure of 100 Pa. What is the mass of the box? Pressure=F/A, Pressure= 100 Pa, F=? A= 0.60mx0.40 m= 0.24 m2 F= P X A= 100x0.24= 24 F= mass X g= 24= mass X 9.8 mass= 24/9.8 = 2.45 kg 8-‐ A 3 kg cylinder has a radius of 12 cm and a height of 1.5 meters. Find the pressure the cylinder exerts on the ground. Area of circle= π r2 Where r= radius P = F/A = (3kg) (9.8 m/s2) / [ π (0.12m)2 ] = 649.9 Pa 9-‐ A swimmer is floating on his back on the sea surface. If his density is 980 kg/m3 and he has a volume of 0.060 m3, what is the buoyant force that supports him in the sea water of density 1025 kg/m3? Density = mass / volume 980 = m / 0.06 = 58.8 kg so…Weight= mass X g =58.8X9.8 = 576.24 N. If something floats then the buoyant force is equal to the weight of the object!! 10-‐ A piece of metal weighs 800 Newtons in the air and 500 Newtons in the water. a.
Find the buoyant force. Hint: Many students miss this easy one on the test) Fb = Wo – Wapp = 800 -‐ 500 N = 300 N b.
Find the volume of the metal VF = Fb / ρ g = 300 N / [ (1000 kg/m3) (9.8 m/s2) ] = 0.0306 m3 c.
Find the density of the metal ρ = m / V = (W/g) / V = [ ( 800 N / 9.8 m/s2 ) / 0.0306 m3 ] = 2667.7 kg/m3

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