弹簧Ablockofmass0.711kgonaspringwithspringconstant239.1N/moscillatesverticallywithamplitude0.563m.Whatisthespeedofthisblockatadistanceof0.329mfromtheequilibriumposition?Alargeair-filled0.271-kgplasticballis

题目详情

弹簧
A block of mass 0.711 kg on a spring with spring constant 239.1 N/m oscillates vertically with amplitude 0.563 m.What is the speed of this block at a distance of 0.329 m from the equilibrium position?
A large air-filled 0.271-kg plastic ball is thrown up into the air with an initial speed of 11.3 m/s.At a height of 3.23 m,the ball's speed is 2.83 m/s.What fraction of its original energy has been lost to air friction?

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答案和解析

第一题比较复杂
首先求新平衡点位移x
Mg=kx 得到新的平衡点为x=0.029
再用能量守恒
0.5kx*2=mgh+0.5mv*2+0.5kx'*2
最终V是8.45m/s
第二题简单些,能量差等于空气阻力造成的能量流失
（0.5mv*2-mgh-0.5mv'*2）/E0 就好
最终能量流失44.14%

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