PHYSICS MCQ DOUBT PLZZZ HELP!!!

[sj0007]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s12_qp_11.pdf

Q12 .....the answer is A....???

Also Q15.....the answer is D....???

 

[sj0007]

Also question number 13 and 14 of http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s12_qp_12.pdf
whose answers are A and B respectively....

 

[SomeStudent]

Also question number 13 and 14 of http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s12_qp_12.pdf
whose answers are A and B respectively....

In 13, we will solve it through two simultaneous equations
W-T=ma (for the 2.0 kg mass) As this mass is pulled down due to its weight. The resultant force acting on it will be W-T as W is greater. There is no component of weight acting in the direction of motion for the 8 kg mass, therefore it will move when the other mass moves down.
T-F=ma (for the 8 kg mass)
F is the frictional force. T is cancelled out. Solve for a which is 1.36. Closest answer is A.

For 14, on sliding down, friction will be opposite motion i.e it will act UP. There is also a reaction force of the wall on the ladder. So these two forces are acting on a point. Find their resultant which gives us the arrow with the direction shown in B. There will be no frictional force for the ground as it isnt rough.

 

[kingo44]

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