Posted by **zachary** on Friday, June 19, 2009 at 6:49am.

these are two similar kinematics maths question which i dont know. Please help!

1)A particle moves in a straight line so that its distance, s metres, from a fixed point O is given by s = 2t^3 - 3t^2 - 12t + 6, where t is the time in seconds after passing O. Find the minimum speed attained by the particle

2)A particle moves in a straight line so that its distance, s meters, from a fixed point is given by s=t^3(2-t)^2, where t is the time in seconds after passing through the fixed point. What is the greatest distance travelled by the particle?

- kinematics -
**Writeacher**, Friday, June 19, 2009 at 7:43am
Bailey, Andrea, Danny, Riley, anabelle, holly, LILLY, zachary, I'm stumped -- or whoever!

To quote one of our very good math and science tutors: “You will find here at Jiskha that long series of questions, posted with no evidence of effort or thought by the person posting, will not be answered. We will gladly respond to your future questions in which **your thoughts** are included.”

- kinematics -
**drwls**, Friday, June 19, 2009 at 7:46am
1) The speed at time t is

|ds/dt| = |6t^2 -6t -12|

(Speed is always positive)

The minimum value of |ds/dt| is 0 if there is a time when

6t^2 -6t -12 = 0

t^2 -t -2 = 0

(t-2)(t+1) = 0

So there IS a time when the speed is zero.

2) The greatest value of s occurs at a time where ds/dt = 0 is the second derivative d^2/dt^2 at that time is negative.

s grows without bound for very large t greater than 2. I do not see how there could be a greatest value of s unless you restrict the region of consideration to 0 < t <2

t = 2

- kinematics -
**drwls**, Friday, June 19, 2009 at 8:43am
In my answer to 2), "is" should be "if".

Sorry about that

## Answer this Question

## Related Questions

- maths urgent please - a particle moves in a straight line such that its position...
- calc-kinematics - if a particle moves along a line so that at time t where t [0,...
- calculus - A particle moves in a straight line with velocity given by v(t) =sin ...
- Physics - Which of the following best describes kinematics? a) Kinematics is a ...
- Physics - I'm having trouble relating Work, with Electric Field, with Kinematics...
- Mathematics - a particle moves in a straight line such that its position x from ...
- mathematics :integration - A particle moves in a straight line through a fixed ...
- mathematics : intergration - A particle moves in a straight line through a fixed...
- Physics - A particle moves in a straight line so that its position (x cm) from a...
- Calculus - A particle moves on a vertical line. Its position, s, in metres at t ...

More Related Questions