Sunday, February 1, 2009
Topic 1:
To appreciate our limited water resources, you are given a map that shows the MacRitchie reservoir. How do you estimate the volume of water available during the dry season when the average depth of water is 2.5m ?
Solution 1:
Area of cuboid = Length x Breadth x Height
1cm --- 60 000cm
Depth: 250cm
Length: 120 000cm
Breadth: 84 000cm
250 x 120000 x 84000
= 2520000000000 cm
= 2520000000000ml= 25.2 giga ml
Solution 2:
Area of cylinder: π x radius x radius x height
radius : 125cm
radius : 125cm
height : 15000cm
π: 3.14
3.14 x 125 x 125 x 15000
=7359375 thousand ml
NOTE: 1 ml = 1cm (http://www.unitconverters.net/)
Topic 2:
You are given a length of copper wire with a small diameter. The only instrument available ot you is the metre ruler. Explain how you would measure the diameter of the wire with an acceptable degree of accuracy.
Solution:
l = nd
l --length of coiled wire
n --number of turns
d --diameter
(The thickness of the wire is its diameter)
Example:
There are 4 turns. The length of the coiled wire is 4 cm.
4 cm = 4 d
d = 1cm
You are given a length of copper wire with a small diameter. The only instrument available ot you is the metre ruler. Explain how you would measure the diameter of the wire with an acceptable degree of accuracy.
Solution:
l = nd
l --length of coiled wire
n --number of turns
d --diameter
(The thickness of the wire is its diameter)
Example:
There are 4 turns. The length of the coiled wire is 4 cm.
4 cm = 4 d
d = 1cm
Topic 3:
In a production line, 10,000 small screws are to be sorted into packs of 50 each. Manual counting would be too tedious. Suggest ways in which the sorting may be done quickly.
Solutions:
1. use an electromagnet
2. use a weighing scale
Solution 1:
Adjust the resistance of the electromagnet such that it will attract 50 screws. However, this is not possible as when you put the magnet near the pile of screws, it will either attract all the screws or none of them.
Solution 2:
Count 50 screws and place them on the weighing scale. Record the weight down. Take a pile of screws and place them on the weighing scale. Take away of add screws according to the weight of the second pile.
In a production line, 10,000 small screws are to be sorted into packs of 50 each. Manual counting would be too tedious. Suggest ways in which the sorting may be done quickly.
Solutions:
1. use an electromagnet
2. use a weighing scale
Solution 1:
Adjust the resistance of the electromagnet such that it will attract 50 screws. However, this is not possible as when you put the magnet near the pile of screws, it will either attract all the screws or none of them.
Solution 2:
Count 50 screws and place them on the weighing scale. Record the weight down. Take a pile of screws and place them on the weighing scale. Take away of add screws according to the weight of the second pile.
Topic 4:
A beam balance will give you a different mass reading on the moon from that on Earth. A beam balance, however, will give you the same reading. Explain why.
Answer:
A spring balance measures weight in Newton(N) and weight is dependent on gravitational pull
A beam balance measures mass and mass never changes/is constant.
Therefore, the beam balance will give you the same reading as mass never changes.
A beam balance will give you a different mass reading on the moon from that on Earth. A beam balance, however, will give you the same reading. Explain why.
Answer:
A spring balance measures weight in Newton(N) and weight is dependent on gravitational pull
A beam balance measures mass and mass never changes/is constant.
Therefore, the beam balance will give you the same reading as mass never changes.
Topic 5:
A submarine can float on the water surface. It can also cruise below the surface. What special structure of the submarine allows it to operate this way? Explain.
Answer:
There are ballast tanks on the side of the submarine. To sink, the tanks let out air and take in water and to float, the tanks pumps in air, pushing the water out.
Food for Thought:
if a submarine lands on the seabed, why is it unable to move and float again once more?
It is because when the submarine lands on the seabed, the upward thrust is gone and although if can move a little forward, it cannot float up anymore.
+ [ written by SEOWHWEE ] + 12:57 AM