Question

In 1977, Kitty O'Neil drove a hydrogen peroxide-powered rocket dragster for a record time interval (3.22 s) and final speed (663 km/h) on a 402 m long Mojave Desert track.(a) Determine her average acceleration during the race.(b) Determine her acceleration while stopping (it took about 20 s to stop).

Answer 1

Answer:

a) 0.05719 km/s^2

b) 0.00921 km/s^2

Explanation:

average acceleration can be calcuated as follows

$a=\frac{\Delta v}{\Delta t} = \frac{v_f-v_i}{t_f-t_i}$  

a)

- In the initial time ($t_i=0$), just before of race start the rocket is at rest. So $v_i=0$.

- After 3.22 s the rocket reach 663 km/h, So $t_f=3.22 s$ and the $v_f=663 km/h$. We convert units from km/h to km/s to have the same time units (seconds)  the velocity would be:

$663 \frac{km}{h}*\frac{1 h}{3600 s} = 0.18467 km/s$

(take into accoun that 1 h=3600 s)

and acceleration is:

$a= \frac{0.184167 km/s-0 km/s}{3.22s-0s}= 0.05719 km/s^2$

b)

acceleration while stopping is calculate with the same formula but now

-we define the initial time ($t_i=0$) the instant just  before begining the stopping. At this instant the velocity is 663 km/h which is the same as 0.18467 km/s.

-After 20 seconds the rocket stops. So tex]t_f=20 s[/tex]  and $v_f=0$

So, acceleration is:

$a= \frac{0km/s-0.184167 km/s}{20s-0s}= 0.00921 km/s^2$