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# AS Physics doubts... Watch

1. This is part of a question :

""A freely falling object has a speed of 5m/s""

Firstly, is it right to use this value as velocity when it says speed? And if i do use this as initial velocity in my equations, will it be positive or negative?

Ive seen that with forces, positive is the convention for forward /up while negative is the convention for down/backwards. So isn't this supposed to be negative as its acting downwards...?

And also for the equation F=ma, is it true that F is only for the resultant force?

Eg. If a person is running to the right with a force of 5N but a force of 4n is acting to the left. And given that he is accelerating rigtwards at 4m/s^2`, what is the
persons mass?
So is it 1/4 or 4/1 ?

Thanks!
2. (Original post by princejan7)
This is part of a question :

""A freely falling object has a speed of 5m/s""

Firstly, is it right to use this value as velocity when it says speed? And if i do use this as initial velocity in my equations, will it be positive or negative?

Ive seen that with forces, positive is the convention for forward /up while negative is the convention for down/backwards. So isn't this supposed to be negative as its acting downwards...?

And also for the equation F=ma, is it true that F is only for the resultant force?

Eg. If a person is running to the right with a force of 5N but a force of 4n is acting to the left. And given that he is accelerating rigtwards at 4m/s^2`, what is the
persons mass?
So is it 1/4 or 4/1 ?

Thanks!
naturally, people presume up to be positive like the y and x axis for a quadrant graph. as long u keep the forces up and down with the same sign its fine. the answer to ur f=ma is 1/4kg. and yes f represents resultant force =)
3. It doesn't matter which way is +ve or -ve, make it watever you want. But opposite direction is the -ve of the first direction

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