其實我想問咩係work done against friction?係咪姐係一個block以u ms-1 既velocity行(唔係constant velocity)一個有friction既surface度行就=work done against friction ,KE=W.D 0.5xmxv*=W.D 另外我想問係咪constant velocity就冇work done? 同埋下邊條題目其實有冇work done
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A block is pulled along a horizontal bench at a constant velocity of 10 ms-1 by a force of 5 N. What is the work done against friction in 4 seconds
係咪個block以constant velocity,冇net force applied,所以就算幾時都好,都冇workｄｏｎｅ，唔知我咁想有冇錯呢？各位人兄help下我><!!!
問題關於work done
2008-06-11 7:12 am
回答 (2)
2008-06-11 6:41 pm
✔ 最佳答案
Work done = force x distanceNo matter the object is moving at constant verlocity or not, the above formula still holds.
If the object is moving in contant velocity, that means there is no acceleration, i.e. no gain in K.E. Therefore all work done is agaisnt fiction.
In your example. The block is moving in constant velocity so there is no gain in KE.
In 4 sec, the block moved 10 x 4 = 40m
Work done = Fs = 5 x 40 = 200 J
If the block's initial velocity (u) is different from final velocity (v), we have to consider this change in KE. i.e 1/2 m (u^2 - v^2). because some work done is transform to change in KE. However in this case since the block is moving at constant velocity. All work done is against friction. i.e 200J
2008-09-19 5:45 am
收錄日期: 2021-04-29 18:09:43
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