# Tangential and normal

1. Jan 3, 2006

### teng125

an outdoor track is 65m.A runner increases her speed at a constant rate from 4 to 7 m/s over a distance of 30m.Determine the total acceleration of the runner 2s after she begins to increase her speed.

2. Jan 3, 2006

### Integral

Staff Emeritus
Could you show us some of your thoughts. What is the relationship between velocity and acceleration?

3. Jan 4, 2006

### teng125

the relation is dv/dt=a.But how can i form eqn??

4. Jan 4, 2006

### Hootenanny

Staff Emeritus
You have the linear speeds and the distance travelled while accelerating, use the equations of motion to calculate the linear acceleration - remember this is a consant acceleration.

5. Jan 4, 2006

### teng125

may i know what's the eqn of motion that u mean??

6. Jan 4, 2006

### cscott

$$a = \frac{v^2 - v_0^2}{2d}$$

7. Jan 4, 2006

### teng125

is it possible to use acce normal + acce tangential formula??

8. Jan 4, 2006

### Fermat

The formula given by cscott is for the tangential acceleration of the girl going round the track. That is a constant value.
Now you have to find the radial accelerartion, which is not constant. Do you know why ?
Ans: Because ar = v²/r and v is constantly changing (in white)
You have to find the peripheral velocity, or speed, at t = 2 sec. From that find the radial accln. Then use pythagoras' theorem with the tangential and radial accln to get the total accln.