A rock attached to a string swings in a vertical circle. Which free-body diagram could correctly describe the force(s) on the rock when the string is in one possible horizontal position, where is the normal force, is weight, and is tension?

Question

A rock attached to a string swings in a vertical circle. Which free-body diagram could correctly describe the force(s) on the rock when the string is in one possible horizontal position, where  is the normal force,  is weight, and  is tension?

Quizplus · Accepted Answer

In this horizontal position, the tension force (11eb8c7e_f54e_010e_8371_03b32f55037a_TB8847_11) is acting sideways and the weight force (11eb8c7e_f54e_010d_8371_c5621b664bb4_TB8847_11) is acting downwards. The normal force (11eb8c7e_f54d_d9fc_8371_e16a2312bab7_TB8847_11) is not present in this position, as there is no contact with any surface. Therefore, the only force acting on the rock is its weight, which is vertical and pointing downwards. So, the correct free-body diagram is C, which shows the weight force (11eb8c7e_f54e_010d_8371_c5621b664bb4_TB8847_11) pointing downwards and the tension force (11eb8c7e_f54e_010e_8371_03b32f55037a_TB8847_11) acting sideways.

A Rock Attached to a String Swings in a Vertical