In the Fig above, MN is a light uniform meter rule pivoted at O, the 80cm mark. A load of mass 3.00kg is suspended on the meter rule at L, the 10cm mark. If the rule is kept in equilibrium by a string RP, fixed at P and attached to the rule at R, the 20cm mark, then the Tension T on the string is?
A.
3.0N
B.
3.4N
C.
3.5N
D.
6.0N
E.
7.0N
Correct answer is E
T * sin30 × 60 = 3 * 70
: T = 7kg