A small rock with mass 0.12 is fastened to a massless string with length 0.80 to

Question

A small rock with mass 0.12 is fastened to a massless string with length 0.80 to form a pendulum. The pendulum is swinging so as to make a maximum angle of 45 with the vertical. Air resistance is negligible. Part A What is the speed of the rock when the string passes through the vertical position? Express your answer using two significant figures. Part B What is the tension in the string when it makes an angle of with the vertical? Express your answer using two significant figures. Part C What is the tension in the string as it passes through the vertical? Express your answer using two significant figures.

Explanation / Answer

well the tension when it makes an angle of 45 is the easy one it is just mgcos45= .12(9.8)(cos45)= .83 N the tension when it passes through the vertical is a little more complicated... find the two forces acting on the object at that point... force of tension and force of gravity. you know that the sum of all forces equals the mass times acceleration f=ma in this case you have a radial acceleration so you need to solve for it using v^2/r where v is velocity and r is the radius so you have 2.1^2/.8=5.5125 you know that F(tension)-F(gravity)=5.5125m so solve for tension F(tension)=.6615+(.12)(9.8)= 1.84 N mastering physics wants 1.9N though so maybe i made a rounding error

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