Still having a hard time getting over the potential energy? It's usually understandable if you just write "PE_object" when doing the calculation on paper.

What is the real reason for asking this question? Are you having trouble with that?

This post has been edited by Critical_Fallacy: Oct 4 2013, 03:13 PM

Do our stories have any influential impact in your decision making?

Generally, we do homework assignments. More importantly, you've got to understand the main objectives and the teacher's intention of assigning homework to students. Are they particularly helpful? <--- (It's a dangerous question, might not be for everyone, so wise and discreet evaluation is recommended.) If they are Past Exam Papers and you've done them some time ago, it probably reinforce your understanding when you revisit and review the questions & solutions.

I know it can be very frustrating to do the homework especially when it upsets your Revision and Study plan as you are counting down for SPM 2013.

Guess that you have justified it with the sketch diagram on the upper right corner. What else do you want?

Remember this: A good explanation doesn’t contradict established knowledge.

Given that

Vector PQ = (k − 3) i + (1) j

and

Vector PQ is a unit vector. (The hidden message is the magnitude |PQ| = 1)

Therefore,

|PQ| = √(x² + y²)

and you finish the rest...

This post has been edited by Critical_Fallacy: Oct 5 2013, 10:15 PM

To be safe, it can be shown that the magnitude of the resultant force, T = 2F cos 30° by applying the law of cosines on the addition of vectors (construct the parallelogram).

Q9 requires you to calculate the pressure at the base of the tank due to water.

And you seemed to know the formula Pressure = Force (or Weight) / Area.

You have calculated the mass of water (m) is 1050 kg. Can you find the weight of water?

Your approach is correct, but lacking experience.

Try multiply the mass of water with g = 9.8 m/s².

Q3

Purpose:
Find the tension in the rope that holds the hot air balloon in equilibrium (static).

Understanding:
The balloon floats because of the buoyant force (from the surrounding air) exerted on it. Without the rope, the balloon will slowly lift up high into the air, because the pressure difference between the top and bottom of the balloon results in a net force that tends to accelerate an object upwards. That's the buoyancy effect.

Solution:
The tension in the rope = the net force (lift) = Buoyancy force (↑) − weight of balloon due to gravity (↓)

Buoyancy force = Weight of air displaced by the balloon

Can you do Q4 using Archimedes' principle?

The pressure formula P = hρg (for fluid) can be derived from P = W / A.

weight, W = mg

mass, m = ρV

volume, V = hA

In fact, if the question asks for the total pressure below the base of the water tank due to the compression load on the concrete foundation, then the formula P = hρg is not sufficient.

Although your answer B is correct, it is worthwhile to mention that, the weight of water displaced by a fully immersed polystyrene DOES NOT equal to the weight of the polystyrene, unless it floats freely on the water surface.

The weight of the polystyrene is negligible (0 N) because it has very low density.

Thus, we have

Tension = Weight of displaced water − 0.

Assuming that all Polystyrene (P) have the same cross section area, so volume of P3 > P2 > P1.

Since the parameters of water density and standard gravity, g are unchanged, then tension T3 > T2 > T1.

This post has been edited by Critical_Fallacy: Oct 6 2013, 01:02 PM

Just want to be more specific. Because we are calculating the weight of the displaced water, W = mg,

where m, the mass of the displaced water is given by m = ρV, we have W = ρVg.

Therefore, it is easier to reason with the Volume of the displaced water because we can justify the volume of an object by vision alone. For mass, we need to measure since it is a fundamental physical property.

A biconvex lens is used to focus the light. If the lens is partially blocked, the light intensity is reduced. Thus, it affects the brightness of the spectrum of colors as well.

I is correct.

The display of the spectrum of colors depends on the prism, and it DOES NOT depend on the biconvex lens. The white light will still hit the prism and it causes the light to be refracted into full spectrum of colors.

IV is false.

Remember to study the Truth Tables and De Morgan's laws as well. Sometimes you will be asked to simplify a complicated Boolean logic by sketching the Digital Logic Gates usually comprising NAND, NOR, XOR & XNOR.

Thanks for the update. Is flip-flop circuit in the physics syllabus?

A simple flip-flop circuit can be constructed from a pair of cross-coupled NOR gates!



This post has been edited by Critical_Fallacy: Oct 14 2013, 08:32 PM

Permutations of 6-letter code in which the letter U & E are side by side: P(6, U|E)

(1) Use 2 letters :: permutations of U|E :: 2!
UE
EU

(2) Use the remaining 4 letters :: order of 4 out of 5-letter alphabet: S|B|J|C|T :: 5P4
SBJC
SBJT
SBCJ
SBCT
SBTJ
SBTC
...

(3) Ways of arranging 4 out of 5-slot code where the inseparable 2-letter U|E is treated as 1 fixed slot and the order of the slots doesn't matter :: 5C4

U|E _ _ _ _
_ U|E _ _ _
_ _ U|E _ _
_ _ _ U|E _
_ _ _ _ U|E

P(6, U|E) = (permutations of U|E) × (order of 4 out of 5-letter alphabet: S|B|J|C|T) × (ways of arranging 4 out of 5-slot code)

P(6, U|E) = 2! × 5P4 × 5C4 = 1200 different permutations

This post has been edited by Critical_Fallacy: Oct 17 2013, 08:46 AM

How do you justify in choosing "5"? Where exactly does the "5" come from? You have to convince the exam markers that "5" is not your lucky pick or else ½-mark is a goner. In Permutations & Combinations, students are taught to use n!, nPr, nCr, and not supposed to list down all possible variations of things that can be arranged in certain manner. Remember that a Permutation is an ordered Combination. Perhaps, the following criteria are helpful in determining nPr or nCr ::

(1) Repetition is allowed
(2) No repetition
(3) Order doesn't matter
(4) Order does matter

This post has been edited by Critical_Fallacy: Oct 17 2013, 10:14 PM

I suppose if the size of the set is small, you can list down them clearly to show the obviousness!

My brain matter is different from yours. I don't memorize but I do familiarize. It's a kind of backpropagation learning method, similar to the way a child learns to identify a motorcar from examples of 4-wheeled sedan cars.

Could you describe exactly the PROCESS or METHODOLOGY of linking the items you remember to their categories? This way, assymessy might learn better.

This post has been edited by Critical_Fallacy: Oct 18 2013, 06:50 PM