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Suppose you swing a ball of mass m in a vertical circle on a string of length L. As you probably know from experience, there is a minimum angular velocity Ó¬min you must maintain if you want the ball to complete the full circle without the string going slack at the top.
a. Find an expression for Ó¬min

b. EvaluateÓ¬minin rpm for a 65 g ball tied to a 1.0-m-long string.

Short Answer

Expert verified

a) The expression Ó¬min=gr

b) The value of Ó¬min = 30 rpm for the given ball.

Step by step solution

01

Part(a) Step 1: Given Information

mass = m
string length= L.

02

Part(a) Step 2 : Explanation

First draw a free body diagram as below then equate forces

At top point equate vertical force, we get

T=(mv2r)-mg

To avoid slack this force must be greater than or equal to zero

That means

mv2r-mg≥0v2r-g≥0(Cancelingm)v≥rg

Substitute v=Ó¬r

Ӭr≥rgӬ≥gr

So

Ó¬min=gr..............................(1)

03

Part(b) Step 1  : Given information

mass = 65 g ball

Length of string =1.0-m

04

Part(b) Step 2 : Explanation

Substitute the values in equation (1), we get

Ó¬min=gr=9.8m/s21m=3.132rad/sec

Convert into rpm

Ӭ=(3.132rad/s)(12πrad)(60sec1min)=29.908rpm≈30rpm.

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