7/28/2019 Archimedes Principle Questions

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Questions on Archimedes principle

In all the following questions use g = 9.82 air = 1.28kg/m3 and water =1000kg/m3

278. The weight of a metal cylinder was measured using a dynamometer in four

different situations. The cylinder was located in:

a) Air

b) Partly submerged in water.

c) Fully submerged in water.

d) Fully submerged in saline water.

The different experiments gave the following reading on the dynamometer.

1) 14.7N2) 5.9N

3) 6.1N

4) 10.4N

Decide which experiment that gave the different readings.

279. A hot air balloon has a mass of 300kg including the basket. The hot air

inside the balloon weighs 17 000N. Determine the maximum load that the

balloon is able to lift if it displaces 25 000N of cold air.

280. A barge floats inside a water filled dock. The barge is loaded with scrap-

iron. What would happen to the water filled dock, if suddenly all scrap-

iron was thrown overboard, ending up at the bottom of the dock?

281. A lock is always filled to the same level, regardless if its a large boat that

enters the lock or if it is a small one. Does this mean that the pressure on

the lock gate is different depending on the size of the boat that is inside

the lock?

282. A stone has a density of 2.40g/cm3 and a volume of 18dm3. Determine:

The mass of the stone.

The weight of the stone.

The apparent weight of the stone in air.

The apparent weight of the stone in water.

283. A couple of ice cubes floats in a glass of water. Will the water level in the

glass change when the ice cubes has melted?

Practical assignment

Place a tub of water on the kitchen sink so that it balances on the edge of the

washing-up sink. What will happen when letting a cup sail over the part of the

tub thats located over the washing-up sink.

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7/28/2019 Archimedes Principle Questions

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Answers

278. A:1 B:4 C:3 D:2

279. It can carry a load of up to 5kN. Archimedes principle tells us that the

buoyant force is 25kN 17kN = 8kN The weight of the basket is 3kN

280. The water level decreases When the scrap-iron is inside the barge, a volume

of water corresponding to the weight of the barge and the scrap-iron is

displaced, this volume is larger than the volume of the scrap-iron since the

density of iron is larger than the density of water.

281. No, the pressure on the lock gate is always the same, since it only depends

on the water level inside the lock.

282. The mass of the stone is 43kg.

m = stoneV

The weight of the stone is.

Wstone = mg

The apparent weight of the stone in air is 0.42kN.

Wair = airV g

Wair = 1.29 0.018 9.82 = 0.23N

Wapparent = Wstone Wair = 424N 0.23N = 424N

So the buoyancy due to the surrounding air is negligible.

The apparent weight of the stone in water is 0.25kN

Wwater = V g = 1.00 103 0.0018 9.82 = 177N

Wapparent = Wstone Wwater = 424N 177N = 247N

283. No the water level doesnt change. According to Archimedes principle the

ice cubes float by displacing a volume of water equivalent to their weight.

This volume is just the same volume of water that is created when the

ice melts.

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