Month: May 2013

Archimedes Principle – Structure Question 3

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A balloon filled with helium gas has negligible mass. The volume of the balloon is 120cm³. [Density of air = 1.23 kg/m³.Density of helium gas = 0.18 kg/m³]

      1. Calculate the mass of the helium gas in the balloon?

m=ρV m=(0.18)(120× 10 −6 )=2.16× 10 −5 kg

      1. Find the weight of the helium gas?
        W=mg W=(2.16× 10 −5 )(10)=2.16× 10 −4 N

    1. The balloon is then tied to a load of mass m kg, as shown in figure above. The balloon and the load float in the air stationary.

      1. Mark in the diagram, all the forces that acted on the balloon.

      1. Write an equation to relate all the forces in )b) (i).

        All the 3 forces are in equilibrium

Upthrust = Weight of the Load + Weight of Helium Gas

      1. Calculate the mass of the load, m.

Upthrust = Weight of the Load + Weight of Helium Gas ρVg=mg+2.16× 10 −4 (1.23)(120× 10 −6 )(10)−2.16× 10 −4 =m(10) m=1.26× 10 −4 kg

      1. If the string that is tied to the balloon is cut, Find upward acceleration experienced by the balloon?

        Net force acted on the balloon = mg = (1.26 x 10-4)(10) = 1.26 x 10-3N
        Mass of the helium gas, m = 2.16 x 10-5kg

    F=ma (1.26× 10 −3 )=(2.16× 10 −5 )a a= 1.26× 10 −3 2.16× 10 −5 =58.3m s −2

    Archimedes Principle – Structure Question 2

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    Figure above shows a glass tube with cross-sectional area of 10 cm² and mass 10 g. It is filled with lead shots and immerse in water. The tube floats upright in the water. [Density of water is 10 g/cm³]

      1. State the name of this device.

        Hydrometer

      1. State one use of this device in a laboratory.

        To measure the density of liquids.

      1. Explain the function of the lead shots in the glass tube?

        To lower down the centre of gravity of the glass tube so that it does not topple when immerse in water.

      1. The length of the glass tube immerse in water is 12 cm. Calculate
        1. the volume of water displaced by the glass tube

          A = 10 cm²
          h = 12 cm
          Let the volume of water = V
          V = hA = (12)(10) = 120 cm³

        2. the weight of the displaced water.

          Mass of the displaced water = 120g = 0.12 kg
          Weight of the displaced water = mg = 0.12 x 10 = 1.2 N

        1. The glass tube together with the lead shots are then placed inside a container that filled with cooking oil. Again, the tube floats upright.
          1. What can be observed in the part of tube that is immerse in the oil when compared with the condition in figure above?

            Longer

        1. Explain your answer in (b)(i).

          The density of the oil is lower than the water.

          Therefore, the volume of oil displaced is greater than the volume of the water displaced to produce the upthrust of same magnitude.