For a relation F = $\dfrac{m(Δv)}{Δt}$, to hold true, the condition(s) necessary is/are:

1. velocities are equal to the velocity of light
2. velocities are much smaller than the velocity of light
3. mass remains constant
4. both (b) and (c)

both (b) and (c)

Reason — It is observed that the mass of a particle increases with increase in velocity but it becomes perceptible only when the velocity v of the particle is comparable with the speed of light c. At velocities v << c, the change in mass is not perceptible. At such velocities (v << c ), mass m can be considered to be constant. Then Newton's second law takes the form F = $\dfrac{m(Δv)}{Δt}$ = ma.

Thus, for F = $\dfrac{m(Δv)}{Δt}$ = ma to hold true, two conditions are required :

1. velocities are much smaller than the velocity of light
2. mass remains constant.