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$*$R$1-48.$ The block has a mass of $0\mathrm{.}5$ kg and moves within the smooth vertical slot. If the block starts from rest when

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the attached spring is in the unstretched position at $A.$ determine the constant vertical force $F$ which must be applied to the cord so that the block attains a speed $v_B=2\mathrm{.}5\frac{m}{s}$ when it reaches $B$:$s_B=0\mathrm{.}15m.$ Neglect the mass of the cord and pulley.Dont use work and energy.