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Finding the speed of the bob?

  • #1
1.) Homework Statement
A(n) 2.71 m long pendulum is released from rest when the support string is at an angle of 35.8◦ with the vertical.
The acceleration of gravity is 9.8 m/s2 . What is the speed of the bob at the bottom of the swing?
Answer in units of m/s

2.) Relevant equations
Not sure

3.) The attempt at a solution
I tried to do 2.71sin(35.8) and I got 1.585. It's not the right answer. I also tried to do do cos(35.8) but that did not work either. Are there any other equations I have to use to find the speed of the bob?
 

Answers and Replies

  • #2
gneill
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1.) Homework Statement
A(n) 2.71 m long pendulum is released from rest when the support string is at an angle of 35.8◦ with the vertical.
The acceleration of gravity is 9.8 m/s2 . What is the speed of the bob at the bottom of the swing?
Answer in units of m/s

2.) Relevant equations
Not sure

3.) The attempt at a solution
I tried to do 2.71sin(35.8) and I got 1.585. It's not the right answer. I also tried to do do cos(35.8) but that did not work either. Are there any other equations I have to use to find the speed of the bob?
Where does the energy come from that results in the bob having a velocity?
 
  • #3
Where does the energy come from that results in the bob having a velocity?
Does the energy come from the string?
 
  • #4
The best way to solve is to draw a neat diagram and show all the forces acting on the object. This might seem trivial but helps in better understanding of many concepts of physics.
 
  • #5
haruspex
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I tried to do 2.71sin(35.8)
What would the result of that calculation represent? What would its units be?
 
  • #6
What would the result of that calculation represent? What would its units be?
since 2.71 is m I assume it would be m as well not m/s.
 
  • #7
haruspex
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since 2.71 is m I assume it would be m as well not m/s.
Right, so it is not a speed.
What do you know about potential and kinetic energy? Any equations you know of?
 

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