Sign Up For Free

**Join for FREE**,
and start talking with other members, weighing in on community polls,
and more.

Also, by registering and logging in you'll see fewer ads and pesky welcome messages (like this one!)

- Reply to threads, and start your own
- Create reports of your
**campus visits** - Share college
**photos**and**videos** **Find your dream college**, save your search and share with friends- Receive our
**monthly newsletter**

College Confidential’s “Dean,” Sally Rubenstone, put together 25 of her best tips. So far, the "25 Tips from the Dean" eBook has helped more than 10K students choose a college, get in, and pay for it. Get your free copy: http://goo.gl/9zDJTM

sonic pwr
Posts: **769**Registered User Member

a particle moves on the x-axis in such a way that its position at time t is given by x=(2t-1)((t-1)^2)

i know that speed is absolute value of velocity and when velocity is 0 t= 2/3 and 1

so during the interval (2/3 , 1) when is the speed at a maximum??

i know that speed is absolute value of velocity and when velocity is 0 t= 2/3 and 1

so during the interval (2/3 , 1) when is the speed at a maximum??

Post edited by sonic pwr on

## Replies to: how to find maximum speed???

183Registered User Junior Memberv(t) = (2t - 1)(2t - 2) + ((t - 1)^2)(2)

v(t) = (4t^2 - 6t + 2) + (2t^2 - 4t +2)

v(t) = 6t^2 -10t +4

so then to find where speed is greatest, find the critical numbers (where deriv is 0 or undef). and i know i'm working with the velocity eq... so we'll count min's as well as max's to find "max speed"

v'(t) = 12t - 10

0 = 12t - 10

t = 5/6

so plug in 5/6 to velocity

v(5/6) = 6*(5/6)^2 - 10(5/6) - 4

..........= 25/6 - 50/6 + 24/6

..........= -1/6

take absolute value, and the max speed is 1/6 units/sec

i guess you didn't need to know what the max speed was, but i did it anyway. but the t value for the max is 5/6.

-will

769Registered User Member157Registered User Junior Memberabs(v(2/3)) = abs(v(1)) < abs(v(5/6))

K, answer for max speed still occurs at time = 5/6

The particle moves to the left when velocity is negative, so the entire interval, yes.

769Registered User Member157Registered User Junior MemberSo, you see, with the first notation you actually have extremas at the endpoints. Hence why you needed to check if speed was greatest there.

183Registered User Junior Member157Registered User Junior MemberBut c'mon, who is never been guilty of not reading a question completely? =P

769Registered User Member157Registered User Junior MemberSo you move to the left at 2/3<t<1 or (2/3,1).