Projectile Motion Elliott

Definition A projectile is any object that is thrown or released into a gravity field.

Key Concepts The horizontal movement is totally independent of the vertical movement.  The two movements are vector quantities, so they have a direction. The velocities are at 90o to each other. There is a resultant velocity from the two independent velocities. We can analyse the vertical movement using the equations of motion.

Basics

Worked Example An aerobatic pilot is flying at a speed of 70 m s-1 between air-shows at a height of 500 m.  He is hungry and eats a pork pie which he finds utterly unpleasant.  He throws it out of the aeroplane.  a)      How long does the pie take to reach the ground? b)      What is the distance between the point of release and the point at which it hits the ground? c)      What is its speed when it hits the ground?

Solution Horizontal velocity = 70 m s-1 Vertical displacement = -500 m (it’s downwards) Initial vertical velocity = 0 m s-1

Now Use Calculated values

Check Your Progress A girl throws a ball at an upward velocity of 15 m s-1. How high will it go? How long will it take the ball to reach its maximum height? In both questions use g = 9.8 m s-2

Answer

Displacement Time Graph

Velocity Time Graph

Check Your Progress Sketch a SPEED time graph for this velocity time graph:

Throwing an Object at an Angle

Calculating Time On release, the arrow leaves at a velocity v m s-1 and angle θ.  The horizontal velocity is v cos θ m s-1 .  The horizontal velocity remains constant at v cos θ m s-1.

Check Your Progress A javelin thrower throws a javelin at a velocity of 25 m s-1 at an angle of 40 degrees.  What distance will he throw the javelin?  Use g = 9.8 m s-2

Answer