Final answer:
There are two values of t for which the particles have the same velocity.
Step-by-step explanation:
To find the values of t for which the particles have the same velocity, we need to find the derivative of their respective position functions with respect to time. Taking the derivative of x1 = sin t, we get v1 = cos t. Taking the derivative of x2 = e-2t - 1, we get v2 = -2e-2t. Setting these velocities equal to each other, we have cos t = -2e-2t. Solving this equation, we find that there are two values of t for which the particles have the same velocity.