OnRamps Physics Practice Test

When gravity is constant and upward is taken as positive, the vertical acceleration is downward and equal to -g. With constant acceleration, velocity changes linearly in time: v_y(t) = v_y0 + a_y t. Substituting a_y = -g gives v_y(t) = V0y - g t. This form matches the initial condition that at time zero the vertical velocity is V0y, and it shows that the upward velocity decreases by g each second due to gravity, eventually reaching zero at the top of the trajectory and becoming negative as the object falls. The other expressions don’t fit the situation: one would imply gravity is acting upward, which is incorrect; another would flip the initial sign of the velocity; and the last uses t^2, which is appropriate for displacement, not velocity (the displacement is y = y0 + V0y t - (1/2) g t^2).