Extra Explaining Questions - MEASUREMENT

MEASUREMENT

1. When answering exam question a student wrote the following.
   ‘A cork floats on water because it is lighter than water. A stone sink because it is too heavy to floats on water’
   Correct the mistakes in the student’s answer.
   [Show answer]

   A cork floats in water beacuse its density is less than that of water. A stone sink in water because its density is larger than that of water
2. Explain the effect observed when kerosene is mixed with water in a beaker. Give a reason to support your answer.
   [Show answer]

   Kerosene will float on water because its density is less than the density of water.
3. Why bodies weigh more when in on the Earth’s surface than when is on the Moon’s surface?
   [Show answer]

   This is because the pull of gravity on the moon’s surface is lower than that on the Earth’s surface. The pull of gravity on the moon’s surface is about 1/6 of that on the earth’s surface.
4. Why does 1 kg of water have a smaller volume than 1 kg of steam?
   [Show answer]

   The molecules of water are close to each resulting to higher density while molecules of steam (gaseous state) are far away resulting to low density. Hence the density of water higher than the density of steam, that’s why 1 kg of water have small volume than 1 kg of steam.
5. You have given kerosene, water, spring balance, beaker and stone. Explain how to determine the relative density of kerosene.
   [Show answer]

   1. Measure weight of a stone in air using spring balance, (W_a)
   2. Pour water of a known volume in a beaker
   3. Measure weight of the stone when immersed in water, (W_w)
   4. Replace water by kerosene in the beaker.
   5. Measure weight of the stone when immersed in kerosene, W _l
   6. Determine the relative density by calculating the ratio of Upthrust in kerosene to the Upthrust in water $$ Relative Density = \frac {W_a - W_l}{W_a - W_w}$$
6. Explain the fact that a body on the moon has the same mass as, but would register less on a spring balance than, the same body on the earth. Explain the spring balance shows this difference and why the beam balance or level balance would not.
   [Show answer]

   A body on the moon has the same mass as on the Earth because mass does not change with gravitational force but weight (measured by spring balance) varies with altitude due to change of gravitational force.

   • Because of reduced gravitational acceleration on the moon of about ¹/₆ of that of that on the Earth, the weight on the moon is less than that on the Earth.
   • Hence difference in readings in spring balance are caused by variation of weight affected by gravity while beam balance of level balance will show same reading because mass does not change or affected by gravity.
7. Briefly explain why it is advised to start at the mark beyond 1cm when taking a measurement using a meter ruler.
   [Show answer]

   It is advised to start at the mark beyond 1 cm when taking a measurement using metre-rule because the rule could be worn out in the ends. It helps reduce zero errors due to imperfection or wear that cause the zero mark to be slightly offset.
8. You have been appointed is an expert in measurement to determine the density of Gemstone extracted at Muhuwesi mine site. How will you accomplish this task?
   [Show answer]

   By using method of immersion

   1. Measure the mass of gemstone using a beam balance, (m)
   2. Pour water in a measuring cylinder and record the initial volume water, (V₀)
   3. Immerse the gemstone in the measuring cylinder containing water then record the new volume of water, (V₁)
   4. Determine the volume of gemstone which is equal to volume of displaced water, (V₁ - V₀)
   5. Determine the density of gemstone using formula $$ Density = \frac {m}{V_1 - V_0}$$