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

The position vector of a particle is given by r= ihat(2t^3-21t^2+60t+10) +jhat(3/2)(t^2-10t+9)

At what time, if any, is the velocity of the particle zero (ie what time is the particle instantaneously at rest)

2. Relevant equations

3. The attempt at a solution

Finding the velocity vector is simple, just taking the derivative of position

However, when I set that to 0 I have the ihat and the jhat and I don't know how to combine them to solve for the time. Is this even the right step?

If I take

v= (6t^2-42t+60)ihat+(3t^2-15)jhat

and set that to 0

how do I account for the vx and vy when setting that to 0?

Do I set vx and vy to 0 separately?

I'm really confused.

Thanks.

**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: 2d Motion, calculating time when v=0 from position vector

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