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[Phy] mechanics(88ALQ2&07ALQ2)

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mechanics(88ALQ2&07ALQ2)

88ALQ2
A smooth block of mass 2 kg slides down a wedge. The wedge, of mass 10 kg, is placed on a horizontal table, and its inclined plane makes an angle of 30º with the horizontal. If the wedge remains stationary all the time, the normal reaction of the table acting on the wedge is
Ans:115N (20cos30cos30+100)
07ALQ2
A wedge of mass M is fixed to the ground. A block of mass m slides down the wedge with constant velocity. What is the normal reaction exerted by the ground on the wedge?
AnsM+m)g

Why the method of calculation is different?How to decide which method should be used?
   

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88ALQ2
smooth block = > move with const acceleration
=> no friction
07ALQ2
const. velocity => friction

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Why the method of calculation is different?How to decide which method should be used?
Thanks

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引用:
原帖由 qwer 於 2016-4-16 09:15 AM 發表
Why the method of calculation is different?How to decide which method should be used?
Thanks
沒有different, 問題應該出於你沒有清楚地畫好free body diagram就去計, 你試下畫下free body diagram先啦

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