匿名使用者
匿名使用者 發問時間: 社會與文化語言 · 1 0 年前

請教大量力學物理題.有答案.但如何計算? 第一篇

因為小弟使用英語教學.但可是我的英語不是很好.如果可以 希望 盡量使用中文解答小弟.謝謝

1 : a sphere X of mass of m travelling with speed u makes a head-on collision with a similar sphere Y which is at rest .After ther collision the velocities of X and Y are a and b respectively .Which one of the following is a possbile pair of values for a and b?

其實是選擇題.但其實我想知道如何計算出答案.所以我想.我列出所有選擇也好像沒有意思=.="希望不要介意

答案

a = u/4 b = 3u/4

2 :

in an elastic collision between 2 bodies , and in the absence of external forces

A : kinetic energy and momentum are both conserved

B : kinetic energy is not conserved but momentum is conserved

這題我選了A但答案是B

elastic collision不是完全守恆嗎?

perfectly elastic collision 與它有什麼分別?

3 : a lift of mass M carries a man of mass m .When the lift is being hauled upward by a rope ,the lift rises with an acceleration a .The reaction between the man and the floor of the life is?

答案是m (g+a)

g 是重力加速度

4 : An object of mass 3 kg is placed on a smooth plane inclined at 30° to the horizontal.It is connected by a light string passing over a frictionless pulley to another object of mass 2 kg Given that g (重力加速度) g = 10 ms ^-1

when the system is released , the tension in the string will be ...?

圖 [url]http://www2.hkedcity.net/sch_files/a/sgs/sgs-s3a/p...

答案 18N

5 :

steel ball bearings .each of mass m are fired at the rate of n ball per second towards a fixed vertical steel block with a horizontal speed v .they rebound from the block with the same speed . The average force exerted on the block is?

答案 2mnv

希望妳們能給我計算步驟..

希望各位能幫助小弟.不要計較點數.小弟的點數真的不多

1 個解答

評分
  • ?
    Lv 7
    1 0 年前
    最佳解答

    1. 固體碰撞在沒有外力影響下動量守恆,因X和Y質量同為m,故mu=ma+mb,或u=a+b.2. 動量守恆不代表動能也守恆,以上題為例,mu=ma+mb,u=a+b,動能 mu2/2=m(a+b)2/2=ma2/2+mb2/2+2mab,所以數學上只有a=0或b=0時動能守恆才成立.物理上動能跟溫度有關係,如果兩個動能不同的物體碰撞發生能量轉移而動能不變,那是一物對另一物做功,已牽涉到外力,就不是彈性碰撞了.3.上舉力克服重力後又提供a的加速度,等於淨加速度g+a,所以施予人的淨力為m(g+a).4.應力的垂直分量為(2-3sin30o)g=5N,應力的水平分量是(3-2)gcos30o=10(3)0.5N,應力和=(52+(10*30.5)2)0.5=3250.5=18.03 N5.動量守恆,鐵板承受的壓力=每秒的動量轉換=n*(mv-(-mv))=2nmv

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