posted by tom .
A child operating a radio-controlled model car on a dock accidentally steers it off the edge. The car's displacement 0.58 s after leaving the dock has a magnitude of 7.1 m. What is the car's speed at the instant it drives off the edge of the dock?
What do you mean by displacement? Horizontal distance from the edge, or the actual slant distance (the resultant of vertical and horizontal components) from the edge?
I will assume the latter, since you refer to the magnitude.
In 0.58 s, the car will fall
Y = (g/2)*t^2 = 1.648 meters
The horizontal distance it will have moved is then
X = sqrt[(7.1)^2 - (1.648)^2] = 6.91 m
The car's speed at the edge would be
X/t = 6.91/0.58 = 11.9 m/s