# Finding the speed of the bob?

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

gneill
Mentor
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?

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

Does the energy come from the string?

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
Science Advisor
Homework Helper
Gold Member
2020 Award
I tried to do 2.71sin(35.8)
What would the result of that calculation represent? What would its units be?

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
Science Advisor
Homework Helper
Gold Member
2020 Award
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?