The mass is rising with a constant speed.
=> So it has no vertical acceleration.
=> So there is no net vertical force acting on it.
=> So the sum of the vertical forces on it is zero.
There are two vertical forces acting on the mass.
=> the force of gravity, pulling it down
=> the tension in the cable, pulling it up.
The force of gravity acting on the mass (its weight) is (mass) x (gravity).
=> That's (120 kg) x (9.8 m/s²) downward.
=> That's 1,176 newtons downward.
If the vertical forces add up to zero, the other force ... the tension in the cable ... must be the same magnitude in the opposite direction.
=> The force of tension in the cable is <em>1,176 newtons upward</em>.
