O-Level Physics

[Volcano123]

Can someone also help me with this question and explain to me the concept? Thank you.

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[Dr.033430Daniel]

Volcano123:

Can someone help me with physics questions and explain your concept? Thanks

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The answer is D. Whenever doing kinematics problems with falling bodies, it is important to pick a direction (up or down) and call it either positive or negative. Here we call upwards positive and downwards negative. I say that because this is the only possibility that fits the answers.

Since the hot air balloon is rising when the bag is released, the initial velocity is up or positive. Remember that if the bag is released from the balloon as the balloon is rising, then the bag has that same upward initial velocity. The bag then rises for a while until it gets to 0 velocity, then it starts to fall back down, so the velocity becomes negative. The graph has a constant gradient which is the acceleration of gravity (so long as there is negligible air friction).

Note that if the question asked about speed, then choice B is the answer. Speed is a scalar quantity and has no direction associated with it, whereas velocity is a vector quantity and has both magnitude and direction (direction being indicated by + or - ).

You could also arbitrarily choose upwards as negative and downwards as positive. So there is another possible answer to this question although it is not one of the choices.

[chubby08]

krz:

Dear all.

My dd is in temasek jc, ip yr 3.
She needs help in physics.
Is anyone giving / intending to give, tuition ?
Or know of anyone who is doing it ?
Really need some help , n references.
Thank in advance.

I have PM you.please check.

[tricia12]

Haha hey chubby08… I know that an ex-TJC Physics teacher recently left TJ… you interested?

[Yan Li]

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[MentalOfSteel]

this question is from 'all about physics' o level theory workbook :

action of 3 forces for 2-dimensional cases & components of force
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thank you so much for explaining the concept

[tutor76]

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[Dr.033430Daniel]

Here is an answer to Mental of Steel's question. I saw this type of question from no less than 5 different schools on either CA1 or SA1 for Sec 3 in 2015 and I expect it to be a popular exam question for Sec 3 in 2016. We have these kinds of questions in our tuition center worksheets because we are constantly updating with the recent school questions.


Here is the question:
http://physicsandcalculus.com/wp-content/uploads/2015/11/scale-diagram-question.jpg\">

The most important thing to realize about this question is that you cannot use the original drawing for a scale diagram. The reason why is that the 500N force is in a rope that is longer than the rope containing the 866N force. That's possible by the way. Just because I have a shorter rope doesn't mean that the tension, or the force within that rope, has to be less. It could be more.

So we must redraw the problem and we redraw using the tip to tail method of vector addition. You use a protractor. Take a scale of say 1cm = 100N. First, draw the 866N force being 8.7 cm long with a ruler and use a protractor to draw it at the correct angle. Then start at the tip of the 866N force, draw a horizontal line (dotted red line), measure the correct angle and draw the 500N force as 5.0 cm. Then you draw the resultant force in black as shown. Measure it with your ruler and it should come out to about 10.0 cm. This is 1000N according to our scale. That resultant upward force is also equal to the weight downward. The resultant force is acting directly opposite the weight, so there is no angle with respect to the vertical, it is exactly vertical.

http://physicsandcalculus.com/wp-content/uploads/2015/11/answer1.jpg\">

So the answers are:
Scale: 1cm = 100N
Magnitude of Resultant Force: 1000N
Direction of Resultant Force: Exactly Vertical
Weight: 1000N

So then you can verify your answer with trigonometry. There are two ways to verify the answer. One using the trig components and the second if you can see the resultant is the hypotenuse of a right triangle. So for those of us who may not have the artistic skills of Leonardo Da Vinci, we can make sure the darn drawing comes out right by doing the side calculation. So your resultant vector should come out to about 10.0 cm.

[Newtandcucumber]

Hi, can anyone who is familiar with the Singaporean Physics O level, advise if the new Physics Higher GCSE, done here in the UK, is easier or harder than your o level. Please look at the Specimen Higher Paper only. The URL is below:


http://www.aqa.org.uk/subjects/science/ ... -resources

[Newtandcucumber]

Anyone, can you respond to my previous post as I am trying to work out if my ds can rehearse SG Olevel papers for the the new UK GCSE