O-Level Physics

[shurley197323]

Can someone help this question pls?


http://i62.tinypic.com/ou4cba.jpg\">

[shurley197323]

Please help!!!


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

[Dr.033430Daniel]

shurley197323:

Can someone help this question pls?


http://i62.tinypic.com/ou4cba.jpg\">

The key to this problem is to understand that the weight of the beam is supported by the vertical component of the tension only. That vertical component is 4/5 times the tension of 1.20kN which equals 0.96 kN.

The force that the hinge exerts on the beam is the reaction force to the tension in the cable pulling horizontally. The tension pulls to the left horizontally, so the force that the question asks for is directed to the right. This is a 3-4-5 triangle, so this force is 3/5 times 1.20kN which equals 0.72kN.

The horizontal and vertical components of the tension can be thought of separately and they do not influence one another.

This question represents an important concept tested at A'Level and also in upper secondary in many IP schools. I've seen a few schools give this type of question for express O'Level physics also. It seems to be popular this year and is making the rounds in many schools.

[Dr.033430Daniel]

shurley197323:

Please help!!!


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

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.

http://physicsandcalculus.com/wp-content/uploads/2015/03/Moments-Question-March-20151.jpg\">

[shurley197323]

Thanks, appreciate your help!

[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.

[physicscher]

Might be able to help. Sent you a PM.

[Volcano123]

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

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[Volcano123]

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

http://i59.tinypic.com/2qvghza.jpg\">

[Dr.033430Daniel]

Volcano123:

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

http://i58.tinypic.com/n3kqxd.jpg\">

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.