Question

A particle having a speed of 0.87c has a momentum of 10-16 kg·m/s. what is its mass?

Answer 1

The momentum p of a moving particle is the product between its mass, m, and tis velocity, v:
$p=mv$
In our problem, we know $p=10^{-16}~Kg \cdot m/s$ and $v=0.87c=0.87\cdot 3\cdot10^8~m/s=2.61\cdot 10^8~m/s$, and using the relationship mentioned above, we can find the mass m of the particle:
$m= \frac{p}{v} =3.8\cdot10^{-25}~Kg$