PHY!!!－bgdwze3的部落格

標題:

PHY!!!

此文章來自奇摩知識+如有不便請留言告知

發問:

a strong man holds a 500N weight as shown. the ends of the chain make angles of 30? and 60? to the horizontal respectively.(please browse this website to see the figure)http://hk.geocities.com/yee_lamlam/fig3.bmp a)find the tensions T1 and T2 in the chain, the tension T3 in the wire. Neglect the weight of the... 顯示更多 a strong man holds a 500N weight as shown. the ends of the chain make angles of 30? and 60? to the horizontal respectively. (please browse this website to see the figure) http://hk.geocities.com/yee_lamlam/fig3.bmp a)find the tensions T1 and T2 in the chain, the tension T3 in the wire. Neglect the weight of the chain and the wire in your calculation. b) Do you think he can make the chain completely straight by pulling it hard? THX A LOT!!!

最佳解答:

a) T3 = 500 N, since T3 is the only tension attaching the weight. Along the horizontal direction, T1 cos 60o - T2 cos 30o = 0 0.5T1 - 0.866T2 = 0 T2 = 0.577T1..........(1) Along the vertical direction, T1 sin 60o + T2 sin 30o = T3 0.866T1 + 0.5T2 = 500 0.866T1 + 0.5*0.577T1 = 500 1.155T1 = 500 T1 = 433 N T2 = 0.577*433 = 250 N b) Let A be the angle T1 makes with the horizontal. If the chain is to be completely straight, the angle T2 makes with the horizontal will be -A Along the vertical direction, T1 sin A - T2 sin A - T3 = 0 T1 - T2 = T3 / sin A..........(2) Along the horizontal direction, T1 cos A = T2 cos A T1 = T2..........(3) Put (3) into (2), T3 / sin A = 0 T3 = 0 The resultant force acting on the weight will be T3 - 500 = -500 N. So it will fall with a downward acceleration 500N / 50kg = 10 m/s2. Therefore, he cannot hold the weight by pulling the chain completely straight.

其他解答:CD51EBF2FDB84E83