# Gravitational Force problem

Here reads the problem. the equator, near the surface of the Earth, the magnetic field is approximately 50.0 µT northward, and the electric field is about 100 N/C downward in fair weather. Find the gravitational, electric, and magnetic forces on an electron in this environment, assuming the electron has an instantaneous velocity of 7.70 x10^6 m/s directed to the east.

Now for gravitational do i set it up by: (G * m1 * m2) / (d2)? If so what would i use for the distance.

For electric force i assume i set it up by: kq/r^2 ?

And then for magnetic forces i assume i set it up by: qvxB?

Also for the directions, would i use teh right hand rule for each one?

Any suggests towards the right way of doing this would be appreciated. Thanks

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LeonhardEuler
Gold Member
For the gravitational force, if you were to use $$F=\frac{Gm_1m_2}{r^2}$$, then r would be the radius of the earth. However, this is unnecesary since around the surface of the earth the terms $$\frac{Gm_1}{r^2}$$ are nearly constant and given by $g \approx 9.81m/s^2$, so the force is just mg.

For the electric force, $\vec{F}=q\vec{E}$ would be more appropriate.

Fort the magnetic force you have it right. The right hand rule is the way to find the direction of the magnetic force.