Each cable takes half the mass. so half of 5.2kg = 2.6kg 2.6kg x accel due to gravity (9.81ms^-2) = Force (N) This is the force due to gravity of (half) the hanging mass. this force vector points down towards the ground. Every force has an equal and opposite force if the mass the forces act on is stationary. This hanging mass is stationary so there must be an equal force going up. Because the force is in the cables it cant go up (because the cable are on an angle) but the force in the cable must have a vertical component equivalent to this required up force. Draw a right angle triangle, the top side is the cieling, the right hand side is the required up force to hold up (half) the mass. The hypotenuse side is your cable. You know the angle between cieling and cable (42deg). Trigonometry: SOH CAH TOA you have Opposite and Hypotenuse sides so use SOH: sin(angle) = O/H rearrange because you want to find H H = O/sin(42) this is the force required in the hypotenuse side (because we are measuring force vectors not distance), and so force in each cable. TO calc tension (a stress) you need divide this force by the cross sectional area of your cable.