香港特色景點

標題:

force in a plane

發問:

a dice A is placed on another dice B on a small plate.both dice have a mass of 10g. find(i)the force exerted on a by b and (ii) the force exerted on b by the plate in the following cases a)the plate is lifted with an acceleration of 2ms^-2 b)the plate and the dice are left to fall freely.

最佳解答:

(a) Consider dice A, let Fa be the force exerted on it by dice B. Using net-force = mass x acceleration. Fa - (10/1000)g = (10/1000) x 2 where g is the acceleration due to gravity, taken to be 10 m/s^2 hence, Fa = 0.12 N Consider dice B alone, the force exerted on it by dice A is 0.12 N in the downward direction (Neton's Third Law, action and reaction). Hence, Fb - (0.12 + 0.01g) = 0.01 x 2 where Fb is the force exerted on dice B by the plate i.e. Fb = 0.24 N (b) Under free fall, dices A, dice B and the plate are under a downward acceleration of g, the acceleration due to gravity For dice A, we have Fa - 0.01g = -0.01g (the -ve sign on the right indicates that the acceleration is downward, i.e. under fre fall) i.e. Fa = 0 N For dice B, Fb - (Fa + 0.01g) = -0.01g i.e. Fb - (0 + 0.01g) = -0.01g Fb - 0.01g = -0.01g Fb = 0 N

其他解答:

• A question on mechanics
• Berryz工房同℃-ute一問
• 不支持B 快門-

 

此文章來自奇摩知識+如有不便請留言告知