An horizontal metre rule PQR is fixed at P. A force of 5N is placed at the end R to keep the metre rule in equilibrium .If PQ is 40cm. Calculate the tension in the string.

Answer 1

To find the tension in the string, we can use the principle of moments. The principle states that for an object to be in equilibrium, the sum of clockwise moments about a point must be equal to the sum of counterclockwise moments about the same point. Let's choose point P as our point of interest.

Let T be the tension in the string, which creates a clockwise moment about point P. The force of 5N at point R creates a counterclockwise moment about point P.

Clockwise moment: T × PQ = T × 0.40 m

Counterclockwise moment: 5N × PR = 5N × (PQ + QR) = 5N × (0.40 m + 0.60 m) = 5N × 1.00 m

For the meter rule to be in equilibrium, the clockwise and counterclockwise moments must be equal:

T × 0.40 m = 5N × 1.00 m

T = (5N × 1.00 m) / 0.40 m

T = 12.5 N

The tension in the string is 12.5 N.