Two smooth blocks of masses m1 and m2 attached with an ideal spring of stiffness k and kept on a horizontal surface. If m1 is projected with a horizontal velocity ν0, find the maximum compression of the spring.
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Solution
Method 1. Decide system: Block and spring. Observation: No external force acting on system in horizontal direction. Conclusion: Linear momentum as well as mechanical energy of system will be conserved. At the time of maximum compression both the blocks will move with common velocity. Problem solving: using conservation of linear momentum at initial time and at time of maximum compression of spring. Let the common velocity of system be V. Pi=m1ν0+0 and Pf=(m1+m2)V A Pi=Pf⟹m1ν0=(m1+m2)V or V=m1ν0(m1+m2) (i) Now using conservation of mechanical energy. ΔK+ΔU=0 (Kf−Ki)+ΔUspring=0 [(m1+m2)V2−12m1ν20]+12kx2=0 (ii) From (i) and (ii), we get x=[√m1m2(m1+m2)k]ν0