In linear motion, what sign will the velocity have if an object is moving in reverse?

In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. what is the electron's orbital frequency? what is the effective current of the electron?

Why do different substances have diffrent properties

Two charged particles, q1 and q2, are located on the x-axis, with q1 at the origin and q2 initially at x1 = 12.2 mm. in this configuration, q1 exerts a repulsive force of 2.62 µn on q2. particle q2 is then moved to x2 = 18.0 mm. what is the force (magnitude and direction) that q2 exerts on q1 at this new location? (give the magnitude in µn.)