How many electrons (mass `9.1xx10^-31`kg) would balance one Proton (mass `1.67xx10^-27`kg)

Calculate de Broglie wavelength of an electron (m = 9.1 xx 10^-31kg) moving with a velocity of 10^5 m//s .

Find the order of magnitude of the force F exerted by the Sun (mass M=1.99xx10^30 kg) on the earth (mass=5.97xx10^24kg) . Use the formula F=G(Mm)/r^2 where the average distance r between the Sun and the earth is 1.49xx10^11m.G=6.67xx10^(-11) S.I. units.

An electron (of mass = 9.1xx 10^31 kg and charge= 1.6xx 10^-19 coul) moving with velocity V=106 m/s enters into a magnetic field region and is found to describe a circle of radius 10 cm. The magnetic field induction in Tesla is

An electron of mass 9xx10^(-31) kg is revolving in a circular orbit of radius 1.8 xx 10^-12 m in a hydrogen atom. If the electrostatic force of attraction between the proton and electron is 8xx10^(-8) N. Find the velocity of the electron.