(2)水泥運動速度:v = st = 2m4s = 0.5m/s .
(3)水泥由兩段繩子承載,水泥上升2m,繩子自由端移動的距離為s=2h=2×2m=4m。
有用功:W has =Gh=500N×2m=1000J,
總功:w has =Fs=300N×4m=1200J,
滑輪組機械效率:η=W,W合計×100% = 1000j 1200j×100%≈83.3%。
答案:(1)這袋水泥的重力是500N;
(2)水泥袋的移動速度為0.5m/s;
(3)滑輪組的機械效率約為83.3%。