有關work done的問題

ting

A constant force of water is used to raise a box of 1 kg vertically from the ground over 1.5 m. The force has done 30 J of work on the box.

What is the acceleration of the box?


請問work done有否已考慮了weight
計acceleration果陣洗唔減個weight?

sapphire

P.E. gained by the block=mgh=15J
net energy W gained by the block=30-15=15J

W=Fs
F=10N

F=ma
a=10 ms^-2

Since 30J is done by the constant force only, it is required to consider the amount of the P.E. gained by the block.
Also, in this case, F is the resultant force of the block. It is no need to consider the weight of the block when calculating the acceleration.

[ 本帖最後由 sapphire 於 14/6/2007 22:21 編輯 ]