A pendulum bob of mass 50 g hangs from the ceiling of an elevator....

Mass of the bob, $m = 50 \text{ g} = 0.05 \text{ kg}$

Since the elevator is moving downward with a uniform velocity, its acceleration $a = 0$.

The forces acting on the bob are the tension $T$ in the upward direction and the weight $mg$ in the downward direction.

Balancing the forces, we get:

$T = mg$

$T = 0.05 \times 9.8$

$T = 0.49 \text{ N}$