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.
a) What distance above the floor was it dropped?
b) 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
o
67
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) ascending
b) descending
c) at the highest point
What would be the direction of the
ball’s acceleration when it is:
a) ascending
b) descending
c) 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 Motion
A 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 ONE
A 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 TWO
A 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 THREE
An 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)