A cart of mass moves on a horizontal track

PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A cart of mass mm moves on a horizontal track. A constant resistive force FrF_r acts opposite to its motion, reducing its speed from viv_i to vfv_f (vf<vi)(v_f < v_i). Which statement is correct about the work done by the resistive force (Wr)(W_r) and the change in kinetic energy (ΔK)(\Delta K)? (a) WrW_r is negative and equals Ki−KfK_i-K_f (b) WrW_r is negative and equals −12m (vi−vf)2-\dfrac12 m\,(v_i-v_f)^2 (c) WrW_r is negative and equals Kf−KiK_f-K_i (d) WrW_r is positive and equals Ki−KfK_i-K_f

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