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[Phy] force and tension

force and tension

Q1=================================================


Q2=====================================================



THX

[ 本帖最後由 ie77 於 2014-9-30 01:25 AM 編輯 ]
   

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Question 1 Analysis:


1. Firstly, For this kind of questions, there should be
no friction or smooth surface, otherwise, you have to specify the frictions between each block.

2. For HKDSE level, the question will say that the the surface is horizontal and smooth, implying there is no friction between the road surface and the block surface.

3. Secondly, for this kind of questions, the string connecting the bodies is inextensible, implying the acceleration of all blocks are the same!

3. Rules of thumb: Combining all blocks as a whole system, Using 2nd Law: Net Force = Mass x acceleration to find the common acceleration.

4. Consider Block A or Block B separately, Using 2nd Law, substitute the acceleration found previously to find the tension!

You can refer to my notes below to know how to solve the problem.


Answers: Acceleration = 0.36 m s^-2 and Tension = 13.04




[ 本帖最後由 andylai 於 2014-9-30 01:36 AM 編輯 ]
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黎sir, 數學物理經濟組合科學(生物,物理)(化學,物理)奪取5**, 20年補習經驗.導師簡介:

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Question 2 Analysis:
Five steps to deal with Force and motion questions:

Step 1: Draw the free body diagram of the object (e.g. Andy) you have to investigate!

Step 2: Label all external forces in the form of "Force on Andy  by   (   )"

Step 3: Resolving components of forces perpendicular to each other.

Step 4: At rest or constant velocity: 1st Law: Resultant Force = 0 N

Step 5: Accelerate or Decelerate: 2nd Law: Resultant Force = mass x acceleration

Make sure to use +ve and -ve to represent the direction of all forces and acceleration / deceleration.

Please refer to my notes attached to solve your problem:

Answers: Normal Reaction = 100.8 N




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黎sir, 數學物理經濟組合科學(生物,物理)(化學,物理)奪取5**, 20年補習經驗.導師簡介:

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