# Kinetic Energy Question

1. Oct 4, 2007

### eanderson

A 47.7-g golf ball is driven from the tee with an initial speed of 55.4 m/s and rises to a height of 31.2 m. (a) Neglect air resistance and determine the kinetic energy of the ball at its highest point. (b) What is its speed when it is 8.47 m below its highest point?

2. Oct 4, 2007

### hage567

What have you tried? You need to show some effort. What equations/concepts might apply here?

3. Oct 4, 2007

### eanderson

K = (1/2)mv^2 and i need something to help deal with the height part

4. Oct 4, 2007

### hage567

Do you know about gravitational potential energy?

5. Oct 4, 2007

### eanderson

U=mgh... 47.7(-9.8)31.2 =14584.754 = U or gravitational potential energy

6. Oct 4, 2007

### Staff: Mentor

Mechanical energy (KE + PE) is conserved. Careful with units. (The mass is given in grams, not kg.)

7. Oct 4, 2007

### eanderson

.0477(-9.8)(31.2) = -14.584752

8. Oct 4, 2007

### eanderson

wouldnt kinetic be 0 at the highest point because all the energy is potential?

9. Oct 4, 2007

### Staff: Mentor

No. Only the vertical component of velocity is zero at the highest point--it's still moving horizontally.

10. Oct 4, 2007

### eanderson

what do i do now?

11. Oct 4, 2007

### Staff: Mentor

Compare the initial energy (KE + PE) at the start with the energy (KE + PE) at the top. The ball loses KE as it gains PE.