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Transcript of Projectile Motion
acceleration in a projectile
horizontal and vertical vectors
effec ts of gravity and air resistance
What is a projectile?
object only acted on by the force of gravity
acceleration is always downwards and equal to g
horizontal velocity is constant
horizontal and vertical motion are independent of each other
Replace a with g
+ = upwards
- = downwards]
y = displacement
v= velocity after time t
u= initial velocity in an upwards direction
v= u - gt
y = ut - 1/2 gt2
g is always downwards and therefore usually negative
t is always positive
u and v can be positive or negative
s can be positive or negative
path becomes steeper as it drops
faster its horizontal projection the further away it will fall
time taken to fall is indpendent od the horizontal speed
A Tile falls from a roof 25m high
calculate its speed when it hits the ground
calculate how long it takes to fall
a car accelerates steadily from rest at a rate of 4.2ms-2 for 6.5 seconds
calculate its final speed
the distance travelled in 6.5 seconds
s= 1/2 gt2
What is it starts at an angle?
lets try to test this?
Sharon fires a scale model of a tv presenter
horizontally with a velocity of 100m/s from 1.5m above the ground.
how long does he take to hit the ground?
how far do they travel horizontally?
A cannonball is fired from ground height at an angle of 40 degrees with an initial velocity of 15m/s
calculate how far the cannon ball takes to hit the ground.
The effects of air resistance
Drag acts on a projectile moving through air
Caused by friction between layers of air near the projectiles surface
Acts in the opposite direction to motion
increases with speed
has a horizontal componenet that reduces horizontal speed and range
reduces maximum height
makes the decent steeper than the accent