4.15. a)
First of all, we need to make an assumption that I weigh about 70 kg. Answers will vary a little due to this. We know that the force exerted by me on the earth and the force exerted by the earth on me are equal and opposite. This can be written
Therefore, we find that the acceleration of the earth is approxiamtely
b)
We want to estimate the distance that the earth moves as I fall toward the floor. This again will require that we make an assumption, here it is that we fall a height of approximately 50 cm from the top of the chair. If we look at how long it takes me to fall the 50 cm back to the earth we find that
In that same time, the earth travels a distance given by
