1. A projectile has been launched across a river, and has just reached the highest
point of its trajectory. Explain why its speed is not zero at this instant.
2. At launch, the velocity of a projectile has a magnitude Vo, directed 45° above the
horizontal. A short while later, the projectile's horizontal displacement is Ax = 20
m. It might seem that, given a launch angle of 45°, the projectile's vertical
displacement at the same instant should be Ay = Ax = 20 m. Explain why its
vertical displacement Ay is actually less than 20 m.
3. A battleship simultaneously fires two shells (projectiles) at two different ships.
Explain why shell B hits its target before shell A. Assume air resistance is
Hint: This is an exercise in thinking about the horizontal and vertical components
of projectile motion separately. Don't consider launch speeds (the drawing gives
no information about them) or launch angle (this doesn't determine flight time
unless you also know the launch speed).
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1) Remember that projectile motion takes place in two dimensions: there is vertical motion and there is horizontal motion. The only force under consideration is the force of gravity, which acts vertically.
Newton's second law, then, tells us that the acceleration in the horizontal direction will be zero ... making the speed constant. Since the horizontal speed at the moment of launch is...