Question

An object is shot from the back of a truck moving at 30 mph on a straight horizontal road. The launcher is aimed upward, perpendicular to the bed of the truck. The object falls:


a in front of the truck
b depends on the initial speed of the object
c behind the truck
d depends on the value of g
e on the truck

the answer is e... why?

Answer 1

Vertical motion and horizontal motion of an object can be analysed independently of one another. Initially, the object is moving along with the truck at 30 mph. Ignoring air friction, when the object is launched vertically, it continues to move forward at 30 mph as it travels upward and then downward under the influence of gravity. Assuming the truck maintains its 30 mph speed and direction, the object will land back in the truck because, independently of the vertical motion of the object, both the object and the truck have continued to travel forward at 30 mph.