A 1.45 kg block is held in place against the spring by a 21 N horizontal externa

Question

A 1.45 kg block is held in place against the spring by a 21 N horizontal external force. The external force is removed, and the block is projected with a velocity upon separation from the spring. The block descends a ramp and has a velocity at the bottom. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction is 0.29. The velocity of the block is at C. The block moves on to D, where it stops. In Figure 7.4, the work done by friction between points B and C is closest to:

Explanation / Answer

Energy conservation:

since point B is in smooth surface, so velocity at B = v2 = 2.1 m/s

velocity at C = v3 = 1.4 m/s

so work done by friction between these points = 0.5m(v3^2-v2^2) = 0.5*1.45*(1.4^2-2.1^2)

= -7.105 J (so option C is answer)

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