Answer
(a) T = 0
(b) T = 0
(c) T = 250 N
Work Step by Step
Since the surface is frictionless, the only possible horizontal force is the force from the tension in the rope.
(a) Since the box is at rest, $T = 0$
(b) Since the box is moving at a steady speed, the acceleration is zero. Therefore, $T = 0$
(c) We can use a force equation to find $T$
$T = ma_x$
$T = (50~kg)(5.0~m/s^2)$
$T = 250~N$
