Projectiles have two types of motion at the same time:

Horizontal Vector

An object travels at a constant speed (assuming no air resistance and no other horizontal

forces)

Speed = Distance/Time

Vertical Vector

An object accelerates towards the ground due to

the force of gravity (assuming no air resistance). The

equations of motion should be used.

g = 10 m/s2

The trajectory of an object projected in the Earth's gravitational field is called a parabola.

Examples of projectile motion (under certain circumstances) include: Missiles, cannon balls, golf balls, footballs, netballs, darts and long-jumpers

Tips when doing calculations:

•Treat the horizontal and vertical parts of the motion separately.•Take the acceleration as 10 m/s2

•In many questions the initial vertical velocity (u) will be zero.

Questions1. A stone released from a cliff takes 3 seconds to

reach the water. How far from the cliff will it land if it is given a sideways velocity of 5 m/s, 10 m/s and 20m/s?

2. Toby threw a ball with a sideways velocity of 15m/s from the top of a 45m high tower. Calculate the time the ball took to reach the ground. How far from the foot of the tower did the ball land?

3. A plane flying horizontally at 50 m/s is to drop supplies to a small village cut off by floods. The plane is flying a height of 100m. How far away from the selected target area should the planes captain release the package, if it is to land on the correct spot?

The resultant velocity of a projectile is the vector sum of the horizontal and vertical velocities.

Calculate the resultant velocity of the supplies in question 3 as they hit the ground.

Hints: i, Calculate the vertical velocity as the supplies hit the ground.

ii, Draw a vector diagram of the velocities

iii, use Pythagoras and trigonometry to calculate the resultant velocity (don’t forget the angle!)