(2)拖拉機將物料從坡底拉到坡頂的時間:t = s/υ= 15m/1m/s = 15s？
(3)邊坡高度:h = Sina 30×s = 1/2×15m = 7.5m
將物質拉到坡頂所做的有用功:W has = Gh =×7.5m = 1×105n×7.5m = 7.5×105j。
拖拉機對材料所做的總功:W = Pt = 6×104 W×15s = 9×105j。
機械效率:η= W/W = 7.5×105j/9×105j = 83.3%。
(4)