As Shown in the Figure,a 1 $v 1 = 1.2 \mathrm {~m} / \mathrm { s }$

Multiple Choice

As shown in the figure,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 $v 1 = 1.2 \mathrm {~m} / \mathrm { s }$ as it separates from the spring.The block descends a ramp and has a velocity $v _ { 2 } = 2.1 \mathrm {~m} / \mathrm { s }$ 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 between the block and the rough surface is 0.29.The velocity of the block is $v _ { 3 } = 1.4 \mathrm {~m} / \mathrm { s }$ at C.The block moves on to D,where it stops.How much of the mechanical energy was converted to internal energy between points B and C?

A) -1.8 J
B) -3.6 J
C) -14 J
D) -6.4 J
E) -7.0 J