posted by Thomas .
Each of four particles moves along an x-axis. Their coordinates (in meters) as functions of time (in seconds) are given by:
Particle #1: x(t)=2t^2-4
Particle #2: x(t)= -3t-4
Particle #3: -2t^2-4
Particle #4: 2 *[sq. root (t+1)] -4
Which of these particles are speeding up for 0<t< infinity?
If you consider "speeding up" to be an increase in speed, regardless of direction, then none of the choices is correct.
#2 and #3 accelerate, backwards. The others start out by slowing down.
They may be referring to increasing speed as an increase in V in the positive direction.