# Homework Help: Help please Problem on Acceleration

1. Sep 5, 2004

### shawonna23

The land speed record of 13.9 m/s (31 mi/h) for birds is held by the Australian emu. An emu running due south in a straight line at this speed slows down to a speed of 10.5 m/s in 2.7 s.

What is the direction of the bird's acceleration?

Assuming that the acceleration remains the same, what is the bird's velocity after an additional 3.9 s has elapsed?

2. Sep 7, 2004

### JasonRox

Hint:

$$a=\frac{v_f-v_i}{t}$$

3. Sep 8, 2004

### Beer-monster

Hint: If it slows down it is decelerating i.e negative acceleration

4. Sep 8, 2004

### HallsofIvy

Also, "speeding up" means speed is increasing: acceleration is "positive"- in same direction as velocity.

"Slowing down" means speed is decreasing: acceleration is "negative"- in opposite direction to velocity.