- #1
neoaddict
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Homework Statement
To make a pendulum, a 300g ball is attached to one end of a string that has a length of 1.4m and negligible mass. (The other end of the string is fixed) The ball is pulled to one side until the string makes a 30 degree angle with the vertical, then (with the string taut) the ball is released from rest. Find a) the speed of the ball when the string makes a 20 degree angle with the vertical and b) the maximum speed of the ball. c) What is the angle between the string and the vertical when the speed of the ball is one-third is maximum value?
m=0.300kg
length=1.4m
angle=30 degrees with vertical
vinitial=0 m/s
Homework Equations
ETinitial=mgh
ETfinal=0.5mv^2 + mgh
ETinitial = ETfinal
The Attempt at a Solution
a) I tried using cos20=adj/hyp and isolated adj, and subtracted adj from 1.4 to figure out the distance from the floor to the bottom of the mass on the string. I then tried substituting that answer into the equation above and tried to isolate final velocity without much success. (The answer should be 1.42m/s)
b) I tried doing the same thing as a, except that ETfinal would not have mgh because it would be at its terminal velocity when h=0. The answer should be 1.92 m/s
c) I tried solving this by multiplying all the terms with speed by 1/3, but it requires knowledge gained from the above two questions to be solved. The answer should be 29.5 degrees
Thanks.