Physics
posted by Adam .
an adult 68 kg cheetah can accelerate from rest to 20.1 m/s (45 mph) in 2.0 s. Assuming constant acceleration, (a) find the net external force causing this acceleration. (b) where does the force come from? that is, what exerts the force on the cheetah?

a= deltav/time
F=ma
Doesn't the ground exert force on the cheta? 
i don't get the first equation explain more please

acceleration= changeinvelocity/time.

should i be using the equation you wrote for finding the net EXTERNAL force??

Yes. That is the force accelerating the cheeta.

i got 1366.8 N and i'm asked to round to SF would it be 1.3*10^2?

a= 20.1m/s /2= 10.05m/s^2
F= ma
How did you get that number 1366?
Now, rounding 1366.8 is not 1/3E2
E2 is 100. But you have other errors that need to be corrected. 
i corrected it and i got 683.4 N, does that sounds right? if yes, would it be 6.8E1?