# physics Q ?

The string is L = 109 cm long, has a ball attached to one end, and is fixed at its other end. The distance d from the fixed end to a fixed peg at point P is 67 cm. When the initially stationary ball is released with the string horizontal as shown, it will swing along the dashed arc. What is its speed when it reaches (a) its lowest point and (b) its highest point after the string catches on the peg?

### 2 Answers

- 2 weeks ago
You can answer question (a) easily, but question (b) is going to be hard to do if we don't know where the peg at point P is since you didn't attach a picture of a diagram.

You are dropping the ball from perfectly horizontal. Therefore the potential energy at the beginning is Ep = m * g * h = m * 9.8 m/s^2 * 1.09m. This will all be translated to kinetic energy when it is at its lowest point, so Ep = Ek = 1/2 * m * v^2 = m * 9.8 m/s^2 * 1.09m. the mass of the object cancels out, it doesn't matter. Therefore:

1/2 * v^2 = 10.682 m^2/s^2

v^2 = 21.364 m^2/s^2

v = sqrt (21.364 m^2/s^2) = 4.6 m/s