According to the equilibrium condition: F=mgsinθ+f
N=mgcosθ
From the sliding friction formula: f=μN
From the point of mathematical knowledge:
sinθ=hl
cosθ=l2？ h2l
Combining the above items, substitute the data: f = 240× (1+6) n = 828n.
(2) Analyze the force of the object, as shown in the following figure:
According to Newton's second law: F+mgsinθ-f=ma.
According to the law of uniform and variable speed motion, l = 12at2.
Combining the above items, substitute the data: t =102s =1.58s.
Answer: (1) The worker's thrust during handling is at least 828 N. 。
(2) If the worker pushes the goods down along the board with a moderate thrust of (1), it takes 1.58 seconds for the goods to push from the top to the bottom of the board.