Space Time & Motion A.2 Forces & Momentum (id: 34079c88c)

本题目来源于试卷: Space Time & Motion A.2 Forces & Momentum，类别为 IB物理学

[单选题]
The diagram shows the forces acting on a block as it slides down an inclined plane with constant acceleration. W is the weight of the block, F is the friction force, μd​ is the coefficient of dynamic friction and g is the gravitational field strength. The plane is inclined at an angle θ to the horizontal.

Which expression gives the acceleration of the block?

A. g$\sin \theta$-g$\mu_d\cos \theta$
B. g$\cos \theta$-g$\mu_d\sin \theta$
C. W$\sin \theta$-W$\mu_d\cos \theta$
D. W$\cos \theta$-W$\mu_d\sin \theta$


参考答案:  A


本题详细解析:
$\underline{\text{Explanation}}$: 
To solve this, we should resolve the weight into components along the slope
Component of weight along the slope = $mgsin\theta$
Normal reaction force (R) is given by $mgcos\theta$ Dynamic friction = ${\mu }_{d}R={\mu }_{d}mgcos\theta$
Apply Newton's second law: $F_{net}=mgsin\theta -{\mu }_{d}mgcos\theta =ma$

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