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2012 WAEC Physics Practical Study the diagrams above and use them as guides in carrying out the following instructions. Using...

Physics
WAEC 2012

Study the diagrams above and use them as guides in carrying out the following instructions.

  1. Using the spring balance provided, determine the weight of the object of mass M= 50.0g in air. Record this weight as W\(_{1}\).
  2. Determine the weight of the object when it is completely immersed in water contained in a beaker as shown in the diagram above. Record the weight as W\(_{2}\).
  3. Determine the weight of the object when it is completely immersed in a liquid labeled L. Record the weight as W\(_{3}\).
  4. Evaluate U = (W\(_{1}\) - W\(_{2}\)) and V = (W\(_{1}\) -W\(_{3}\)).
  5. Repeat the procedure with the objects of masses M= 100g, 150g, 200g, and 250g
  6. In each case, evaluate U = (W\(_{1}\) - W\(_{2}\)) and V = (W\(_{1}\) -W\(_{3}\)).
  7.  Tabulate your readings.
  8. Plot a graph with V on the vertical axis and U on the horizontal axis.
  9. Determine the slope, s, of the horizontal graph.
  10. State two precautions taken to ensure accurate results.

(b)i. State Archimedes' principle.

ii.  A piece of brass of mass 20.0g is hung on a spring balance from a rigid support and completely immersed in kerosene from of density 8.0 x 10\(^{2}\)kgm\(^{-3}\).  Determine the readings of the spring balance (g= 10ms\(^{-2}\), density of brass 8.0 x 10\(^{3}\)kgm\(^{-3}\))

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Explanation
M\(_{(g)}\) W\(_{1}\) W\(_{2}\) W\(_{3}\) U=(W\(_{1}\)-W\(_{2}\)) V=(W\(_{1}\)-W\(_{3}\))
50 0.50 0.43 0.45 0.07 0.05
100 1.00 0.90 0.88 0.10 0.17
150 1.50 1.30 1.33 0.20 0.17
200 2.00 1.73 1.75 0.27 0.25
250 2.50 2.15 2.20 0.35 0.30


SEE THE GRAPH ABOVE
Slope, s = \(\frac{y_{2}-y_{1}}{x_{2}-x_{1}} = \frac{0.275-0.10}{0.32-0.125}\)

s = \(\frac{0.175}{0.195}\) = 0.9

Precautions: i
- ensured that I avoided errors due to parallax while taking the readings on the spring balance.
- made sure the mass is totally immersed in water and liquid
- ensured the retort stand and clamp are well tightened.

(b)i. Archimedes' principle states that when a body is totally immersed in a fluid (liquid or gas), it experiences an upthrust that is equal to the weight of the fluid displaced.

Mass of brass = 20g = 2 x 10\(^{-2}\)kg
Density of kerosine 8.0 x 10\(^{2}\)kgm\(^{-3}\)
g = 10ms\(^{-2}\)kg
Density of brass = 8.0 x 10\(^{3}\)kgm\(^{-3}\)kg

Volume of brass = \(\frac{m}{D} = \frac{2 \times 10}{8 \times 10^{3}}\) = \(\frac{2}{8}\) x 10\(^{-2-3}\)

= 0.25 x 10\(^{-5}\)m\(^{3}\)

Volume of brass = 2.5 x 10\(^{-6}\)m\(^{3}\)

Therefore, the mass of brass in kerosene 
m = Density x volume of brass
= 8.0 x 10\(^{2}\) x 2.5 x 10\(^{-6}\)m\(^{3}\)

= 20 x 10\(^{-4}\)

Reading on the spring balance 
20 x 10\(^{-4}\) = 20 x 10\(^{-3}\) N


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