1. Why is it so hard to get rubbish in the bin?

2. Projectile motion Remember Newton’s 1st law of motion
If there is no force acting on an object there is no acceleration, so the object will be stationary or will move at a constant velocity.

3. Definition of a projectile
Any object moving through air without its own source of power and only under the influence of gravity…
eg: a golf ball after being hit.

4. Compare a ball rolling off a desk to one being dropped
The balls land at the same time because the force of gravity is the same on both.
The rolled ball continues moving forward at the same speed as on the desk: there is no horizontal force to slow it down.

5. Key physics ideas for projectiles
Divide the story into horizontal and vertical directions.
There are no horizontal forces acting so the velocity is constant and we use the equation v = d/t.
The only vertical force is gravity so we know the acceleration is 9.8ms-2.
Time of flight is the only thing common to the vertical and horizontal movements.
Use the five equations of motion.

6. Solving Projectile problems: the first type…
Facts about simple vertical projectiles
Throwing something straight up or down
Acceleration is ms-2 on the way up and +9.8ms-2 on the way down
Velocity is 0ms-1 at the top of the motion

7. Q: A tennis player throws up a ball at 5. 8ms-1 for a serve
Q: A tennis player throws up a ball at 5.8ms-1 for a serve. What is the maximum height the ball reaches?
Fill in the information you know
Vi =
Vf =
a =
d =
Choose an equation of motion
Substitute and solve
Use the problem and common sense
Vi = 5.8 ms-1
Vf = 0 ms-1
a = -10 ms-2
d = ?
Vf2 = Vi2 +2ad
0 = (-10)d
d = 1.7m

8. Q: A tennis ball is thrown up at 3. 9ms-1
Q: A tennis ball is thrown up at 3.9ms-1. How long does it take to reach its maximum height? Q: A rock is dropped off a cliff 75m high. How long does it take to reach the bottom of the cliff? What is its speed after 2s?
Vi = 3.9 ms-1, Vf = 0ms-1,
a = -10 ms-2, t = ?
Vf = Vi + at
0 = t
t = 0.398s
d = 75 m, Vi = 0 ms-1, a = -10 ms-2
d = Vit + 1/2at2
75 = 1/2 (-10)t2
t = 3.9s
Vf = Vi + at = 0 +10x2
= 20ms-1

9. Solving projectile problems: the second type
Half projectiles
At position A the velocity is only horizontal
At position B the horizontal velocity is the same but there is a vertical component A B
Range

10. Q: A person fires a gun horizontally from the top of a cliff 70m high
Q: A person fires a gun horizontally from the top of a cliff 70m high. The bullet travels out at 100ms-1. Two possible Q…
What is the time to the bottom?
Since time is the dame vertically or horizontally, use either vertical or horizontal, eg: vertically,
Vi = 0 ms-1, a = 10 ms-2, d = 70 m
d = Vit + 1/2at2
70 = 0 + ½(10) t2
t = 3.7s
What is the range? Must use the horizontal information,
Vi = 100 ms-1, a = 0 ms-2, t = 3.7 s
d = vt = 100(3.7)
= 370m

11. Q: A duck shooter fires a bullet horizontally at 80ms-1 to hit a duck
Q: A duck shooter fires a bullet horizontally at 80ms-1 to hit a duck. They miss, and the bullet comes down 1.8m to hit the ground. Find the time for the bullet to hit the ground and the distance away from the shooter that it lands.
Q: A food crate is dropped from a plane flying horizontally at 160ms -1. If the crate takes 12s to hit the ground, from how high was it dropped. How far does the crate travel horizontally from the point where it was dropped?