## O-Level Physics

PSLE marks the graduation of Primary school students and their entry into Secondary schools as teenagers. Discuss all issues about Secondary schooling here.

### Re: O-Level Physics

A lawn roller has a diameter of 1.20 m and weighs 560N.

a) What is the minimum force needed to push the roller over a brick of height 0.100 m if the force is applied at the centre of the roller?

b) What is the minimum force needed to push the roller over a brick of height 0.100 m if the force is applied at the top of the roller?

Thank you <3

I have answered part a here in this diagram. This is a moments question. The first diagram is showing how to equate the clockwise moment to the anti-clockwise moment. The second diagram is showing how to work out the value of x, the distance of the line of action of the weight from the pivot point.

Dr.Daniel
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### Re: O-Level Physics

shurley197323
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### Re: O-Level Physics

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.

krz
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### Re: O-Level Physics

Might be able to help. Sent you a PM.

physicscher
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### Re: O-Level Physics

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

Volcano123
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### Re: O-Level Physics

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

Volcano123
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### Re: O-Level Physics

Volcano123 wrote:Can someone help me with physics questions and explain your concept? Thanks

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.

Dr.Daniel
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### Re: O-Level Physics

krz wrote: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.

chubby08
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### Re: O-Level Physics

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

tricia12
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### Re: O-Level Physics

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Yan Li
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