A soccer ball is kicked into the air. You may safely assume that the air resistance is negligible. The initial velocity of the ball is 40 ms-1 at an angle of 40o to the ground.

1. Sketch a labelled diagram to show: the initial velocity of the ball; its horizontal component and; its vertical component

2. Find the horizontal component of the ball’s initial velocity.

3. Find the vertical component of the ball’s initial velocity.

A ball is rolling along a flat, level desk. The speed of the ball is 0.3 ms-1. Ignore friction (assume that the ball does not slow down, and the speed is constant).a) How long would it take for the ball to travel 2 m?b) What distance would it travel in 0.4738 seconds?

A ball is dropped and it took 0.4738 seconds to hit the floor.c) What distance above the floor was it dropped?d) What would be the speed of the ball the moment

it hits the floor?

Find the horizontal component and the vertical component of this force vector

30 N

67o

Motion under gravity• Mass vs Weight• What is “g”?

is called the acceleration due to gravity (= 9.8 ms-2, downwards)

This is the acceleration of any object that moves in the air without its own power source (e.g. falling rocks, bullets, shot puts)

A 5 kg rock is dropped from 2 m above…

1. Newton’s Law: 1st or 2nd ?2. What is the acceleration of the falling

rock?3. What is the mass of the falling rock?4. What is the net force of the falling rock?

A 300 kg rock is dropped from 2 m above…

A ball is thrown upwards. Describe the direction of the ball’s velocity when it is;

a) ascendingb) descendingc) at the highest point

What would be the direction of the ball’s acceleration when it is:

d) ascendinge) descendingf) at the highest point

A man jumps off a cliff 50 m above the sea. (g = 9.8 ms-2)

a) What is his initial velocity?

b) What is his acceleration?

c) How far does he fall in one second?

d) How far does he fall in two seconds?

e) How long does he take to fall 50 m?

Green book page 85

A ball is thrown upwards with an initial speed of 20 ms-1.a) How far does the ball rise

in one second?

b) How long does it take to reach the highest point?

c) How high is the highest point from where it started?

The bullet question…

Vertical Motion vs. Horizontal Motion

Projectile MotionA projectile is any object that moves through the air without its own source of power. It is assumed that once in flight, the only force acting on a projectile is its weight force. (air resistance is ignored in this topic)

This means that:

• as the projectile moves, it accelerates constantly downwards at 9.8 ms-2.

• there is no force acting in the horizontal direction, and so the projectile moves horizontally at a constant speed.

For any projectile moving over a horizontal ground:

• At the maximum height of the flight, the vertical component of the velocity is zero.

• Time taken to reach the max height = time taken to reach the ground from the max height.

• The projectile hits the ground at the same speed as it was fired.

Example ONEA car running with a speed of 30 ms-1 plunges into the sea from the top of a cliff 50 m above the sea.a) What is the initial horizontal speed?b) What is the initial vertical speed?c) What is the horizontal acceleration?d) What is the vertical acceleration?e) How long will it take to fall?f) How far away from the cliff will the car

land?

Example TWOA rock is hurled from a catapult. The initial velocity of the rock is 60 ms-1 at an angle of 32o to the ground.a) What is the initial horizontal speed?b) What is the initial vertical speed?c) How long will it take to reach the max

height?d) What would be the total flight time?e) Calculate the horizontal distance the ball

travels during its flight.

Example THREEAn angry basketball player kicks a ball. The initial velocity of the ball is 25 ms-1 at an angle of 45o to the ground.

a) What is the initial horizontal speed?

b) What is the initial vertical speed?

c) What is the total flight time?

d) How high does the ball rise?

e) Calculate the horizontal distance the ball travels.

• Homework Booklet WORKSHEET SIX

• Extension: Activity 11B (Green book pg. 136)