- #36
nasu
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Both g and a are negative (or they are both positive) as long as they are in the same direction - downwards. You need a minus in front of the "ma" term because the friction force is opposite to the weight, not because the acceleration is negative. This is so as long as the acceleration is less than g.
If the acceleration becomes larger than g, the friction force has to acts downwards, otherwise the block will move towards the ceiling of the elevator. The formula for F will change for this case becaue the friction and weight act in the same direction.
If the acceleration becomes larger than g, the friction force has to acts downwards, otherwise the block will move towards the ceiling of the elevator. The formula for F will change for this case becaue the friction and weight act in the same direction.