Question

You take the opportunity to stock up on snacks and head on your way. You wind along the road for quite some time before you find a very dark site and pull of onto dirt road. About 100 meters up the road your passage is stopped by a metal gate. The gate consists of a single heavy bar stretching 6 meters across the road. It looks like schedule 5 stainless steel pipe, of all things, clocking in at about 7 kg/linear meter if you recall correctly. It is hinged on the left side allowing you to lift it upwards. You know from experience that you can lift about 20 kg without much effort. Where should you lift the gate to apply the proper torque to move the bar?

Answer 1

Let us assume to balance the torque of weight of the bar to other end assume the weight of the bar acts at its middle point Thus from the application of weight is 6/2, = 3 m right to left end from the torque formula we can find the weight of the bar tau = Fd = 7 times 6 times 3 kg The capacity of lifting is, 20 kg (without much effort) since to balance the torque of weight means we should apply force at a distance x in meter x = 126/20 = 6.3 m 6.3 m right from the left end of bar Therefore of lift the gate 6.3 m to move the bar