Physics...?

Question

How are acting two forces which are affectring on masses weighting 3 and 5kg, if the both masses have the same velocity?

Answer 1

Can't say. You said nothing about their accelerations.

Remember: F = MA where
F is force
M is mass
A is acceleration

Acceleration is the rate of change of velocity. If the two masses are not accelerating (i.e. their velocity is constant), then the force on each is 0.

If the two masses have the same acceleration, then the forces have to be in proportion to their masses.