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# OCR A2 - textbook further questions A Help watch

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can anyone tell me wht to do for this?

Q4b OCR Physics A2 pg 87

the distance between the centres of the Earth and the Moon is 3.8*10^8m. Assume that the moon moves in a circular orbit around the centre of Earth. Estimate the period of this orbit to the nearest day. Note that 1 day = 8.6x10^4s

at first i thought calculating F from newtons law of gravitation then put it into Centripetal force.... but do I have the velocity of the moon???

thxxx
2. F= GMm/r^2
a = rw^2

GMm/r^2 = mrw^2
GM/r^3 = w^2

should help, it's where keplers law comes from i thnk

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