Randall D. Knight — Dynamics II: Motion in a Plane: Problem 38

A \(2.0 \text{ kg}\) projectile with initial velocity \(\vec{v} = 8.0 \hat{i} \text{ m/s}\) experiences the variable force \(\vec{F} = -2.0t \hat{i} + 4.0t^2 \hat{j} \text{ N}\), where \(t\) is in \(\text{s}\). a. What is the projectile's speed at \(t = 2.0 \text{ s}\)? b. At what instant of time is the projectile moving parallel to the \(y\)-axis?