Answer: 0
Explanation:
75 newtons will push back canceling it out make it 0
It would be 12,000 because newton’s third 2nd law states F=ma (force=matter x acceleration) so 30x400 would be your force .
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For rotational equilibrium of the door we can say that torque due to weight of the door must be counter balanced by the torque of external force

here weight will act at mid point of door so its distance is half of the total distance where force is applied
here we know that

now we will have


so our applied force is 72.5 N
1. Using Strong Permanent. 2. increasing the current. 3. Decreasing the space between Magnets
Explanation:
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