Homework Help: 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.