Calculating the Speed of a Pendulum Bob Using Energy Equations

[Vanessa Avila]

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?

 

[gneill]

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?

 

[Vanessa Avila]

Where does the energy come from that results in the bob having a velocity?

Does the energy come from the string?

 

[ImperialThinker]

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.

 

[haruspex]

I tried to do 2.71sin(35.8)

What would the result of that calculation represent? What would its units be?

 

[Vanessa Avila]

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.

 

[haruspex]

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?