更新1:
When a body which has a mass of 5 kg and accelerate for 2 m/s hits on me, is the force act on me equals 10N, too?
about F=ma
2007-11-21 9:25 am
When a body has a mass of 5 kg and accelerate for 2 m/s, by F=ma, the force is 10N. However, what kind of force is 10N? Is 10N the force needed to accelerate for 2 m/s of a 5 kg object, or the force exerted by the 5 kg object which is accelerating for 2 m/s? My point is that if 10N is the force exerted from or exerted to the object.
回答 (2)
2007-11-21 10:58 am
✔ 最佳答案
First of all, F=ma= (mv-mu)/t,
where m is mass of the object; v is final velocity; u is initial velocity; t is the time of change from u to v
As you said, F is 10N, object is 5kg and v is 2 m/s ( remember is velocity, not acceleration, then
10N = [5(2-0)]/t
Implies that t = 1 sec.
It means that when a object 5kg required to move from steady to at speed of 2 m/s with 10 N. 1 second is required to accelerate.
On the other hand, you may think that when a object 5kg required to move from steady to at speed of 2 m/s in 1 sec, 10N force is required to act on the object.
參考: 恩師傅一紫
2007-11-21 11:22 pm
action = reaction so
1) the force act on the 5kg mass is 10N
2) the force reacted on you by the mass is also 10N
Some points to note:
1) It is wrong to say a force is accelerating! Acceleration and Velocity both can only be used on Mass or Object, A force cannot accelerate.
2) You may think your hand is moving and accelerating rite? but the correct way to consider the force of 10N react on you should be Acceleration = 10N/Mass, where Mass should be your weight -- the whole body if you are in the space, or includes the earth too if you are standing on ground. Since Mass is too large, Acceleration = 0, that's why you and the earth wont move when you push a mass using a force of 10N.
2007-11-23 11:22:04 補充：
This is not a clear question I would say. When a mass of 5kg with a=2 hits you, there are some different cases:1) the mass stopped but the force acting on the mass (10N) is still there.2) the mass stopped but the force acting on the mass (10N) has vanished.3) the mass rebounces
2007-11-23 11:22:27 補充：
Also the force acting by the mass on you is different at different time1) when the mass is decelerating but still in contact with you2) when the deceleration has finished but the mass is still in contact with u
2007-11-23 11:22:57 補充：
For each cases, you can use the combination of these rules to get the force acting on you (I am not gonna to give you the answer, try to work out yourself)1) F1 = ma (a may be deceleration)2) F2 = (mv-mu)/tF1+F2 = force acting on you by the mass
1) the force act on the 5kg mass is 10N
2) the force reacted on you by the mass is also 10N
Some points to note:
1) It is wrong to say a force is accelerating! Acceleration and Velocity both can only be used on Mass or Object, A force cannot accelerate.
2) You may think your hand is moving and accelerating rite? but the correct way to consider the force of 10N react on you should be Acceleration = 10N/Mass, where Mass should be your weight -- the whole body if you are in the space, or includes the earth too if you are standing on ground. Since Mass is too large, Acceleration = 0, that's why you and the earth wont move when you push a mass using a force of 10N.
2007-11-23 11:22:04 補充：
This is not a clear question I would say. When a mass of 5kg with a=2 hits you, there are some different cases:1) the mass stopped but the force acting on the mass (10N) is still there.2) the mass stopped but the force acting on the mass (10N) has vanished.3) the mass rebounces
2007-11-23 11:22:27 補充：
Also the force acting by the mass on you is different at different time1) when the mass is decelerating but still in contact with you2) when the deceleration has finished but the mass is still in contact with u
2007-11-23 11:22:57 補充：
For each cases, you can use the combination of these rules to get the force acting on you (I am not gonna to give you the answer, try to work out yourself)1) F1 = ma (a may be deceleration)2) F2 = (mv-mu)/tF1+F2 = force acting on you by the mass
參考: Myself
收錄日期: 2021-05-02 12:51:03
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