(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Part A

A cheetah, the fastest of all land animals over a short distance, can accelerate from zero to 18.0 m/s in three strides and to a full speed of 31.3 m/s in seconds. Assuming the first three strides are each 4.2 m long and that acceleration is constant until the cheetah reaches full speed, what is the cheetah's acceleration (in m/s2)?

Part B

If in part (a) of this question the cheetah's first three strides were each 4.6 m long, how many seconds would it take to reach its full speed?

2. Relevant equations

3. The attempt at a solution

Ok so for Part A I use the above equation:

31.3^2 - 18^2 = 2*a*12.6 (12.6 = 3 strides)

979.69 - 324 = 25.2a

655.69 = 25.2a

a = 26.02

Ok this is where it gets weird. That is not the answer, but when I divide it by 2, I get 13.01 which is within 0.1 of the answer showing on the online test. Every time I try this question with different velocities, I am within 0.1 of the online test's correct answer. The test gives me the mark, but I can not help but wonder if it's me doing something wrong or is the programming on the online test a bit off.

I am not really concerned about Part A, but Part B I just can't understand. I have tried using the rearranged velocity equations and the simple speed equation, but I still can't get the answer shown. The answer for Part B is 2.67 seconds.

EDIT: Sorry about the attachment, not sure how to make it appear within the post.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Velocity Question - Odd answers

**Physics Forums | Science Articles, Homework Help, Discussion**