Please , Explain me this situation A spider is attached to two threads of equal length that make a 120o angle with each other. The spider is motionless and its mass is m=30mg. What is the tension in each thread? According to the Newton first Law, the sum of the force must be 0. T1+T2+Fspider=0 since the threads are the same length and symetrical, T1=T2. Fspider=-3.0 *10-4N so I found T1=1.5 *10-4N I am surprised to see that the answer is 3.0 *10-4N on each thread please now I am confused! help
Remember you are dealing with forces in 2 axes. X and Y not in 1. I think that is where you made ur mistake. Fyspider=mspider*gravity Since spider is not moving back and forth then Fx=0 which means that |Fxthread1|=|Fxthread2| Since the angle is 120 between them and symectrical we have 30-60-90 triangles created for each thread. Fyspider-2Fythread=0 therefore Fythread=Fyspider/2 Now we need Fxthread, since both at equal, we solve for either. Knowing Fythread, we use the law of sines. Fythread/sin 30 = Fxthread/sin 60 Fxthread=Fythread*sin60/sin30 Fthread=sqrt(Fxthread^2+Fythread^2) Hope that helps.