佢個答案計到距離係24m,但係我用v=u+at計到v=12,
咁我用24/4黎計velocity都唔等如12,唔係話p=fv=fs/t咩??
我想問點解用 power=force x velocity黎計唔得ge???
更新1:
但係power=force x velovity 點解我唔可以直接搵個velocity出黎????
physics-velocity
2008-12-24 6:27 am
A motor car of mass 2000kg accelerates from rest at 3 ms-2 for 4s on a straight road. find the average useful output power of the engine of the car.
佢個答案計到距離係24m,但係我用v=u+at計到v=12,
咁我用24/4黎計velocity都唔等如12,唔係話p=fv=fs/t咩??
我想問點解用 power=force x velocity黎計唔得ge???
佢個答案計到距離係24m,但係我用v=u+at計到v=12,
咁我用24/4黎計velocity都唔等如12,唔係話p=fv=fs/t咩??
我想問點解用 power=force x velocity黎計唔得ge???
回答 (2)
2008-12-24 10:58 am
✔ 最佳答案
In this question, you can use the formula:
Power = Force x velocity
The above formula is suitable for "uniform velocity motion" and "uniform acceleration motion".
In uniform velocity motion, the velocity is a constant. The case is simple.
In uniform acceleration motion, the velocity is varied in uniform acceleration. The velocity used in the above formula is the "average velocity" of the motion, i.e.
Power = Force x (average velocity)
The question involves uniform acceleration motion. Therefore, "average velocity" should be used in the above formula. The average velocity can be calculated in either of the following two ways:
(1) Average velocity = (u + v)/2 = (0 + 12)/2 = 6 m s-1
(2) Average velocity = displacement/time = 24/4 = 6 m s-1
You have made confusion because you took v (the final velocity) as the average velocity.
=
2008-12-24 6:47 am
S = ut+0.5at^2
= 0 + 0.5(3)(4)^2
=24m
Power = force x displacement / time
= 2000x3x24/4
= 36000 W
= 0 + 0.5(3)(4)^2
=24m
Power = force x displacement / time
= 2000x3x24/4
= 36000 W
收錄日期: 2021-04-23 23:05:09
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