Kamala tries to open a door by applying force of 3500gf-cm at the doorknob. If the knob is 60cm from the hinge, what force (in N) should she apply in order to open the door by pushing it at a distance of 25cm from the knob?
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The correct option is A 58.8 Given: Distance between the doorknob and the door hinge, l1=60cm Force applied at the doorknob, F1=3500gf-cm In the second case, force (say F2) is applied at a distance of 25cm from the doorknob, i.e. it is applied at a distance of l2=60−25=35cm from the hinge. According to the principle of moments, F1×l1=F2×l2