Transcript 3. Projectiles - Kelso High School

Drawing distance, speed, acceleration vrs time graphs
NB: The slope of the ramp must stay constant and should be small
mask
LG1 LG2
trolley
ramp
1. Distance verse time
The light gates should be connected to a QED set to gap time.
This measures the time between LG1 and LG2.
Find this time at 5 different distances and draw a graph.
distance
time
2. Speed verses time
Use one light gate and set QED to instantaneous speed.
Measure the speed at the same distances down the ramp as
before. This will allow you to draw a speed time graph.
speed
time
3. Acceleration verses time
Use one light gate and the double mask.
Measure the acceleration at the same distances down the
ramp as before. This will allow you to draw an acceleration
time graph.
speed
time
play
Projectiles
The only force which acts on a projectile
is the force due to gravity ( weight)
We need to resolve the
velocity into its horizontal
and vertical components
v
v
Horizontal velocity
Vertical velocity
vH
vv
Down
+ ve
t
No force in horizontal
direction so constant
velocity
t
Weight acts downward so
accelerates at 9.8 m/s2
down
Example
A car travelling with a horizontal speed of 20 m/s goes off
the top of a cliff. It lands 30 m from the foot of the cliff
(i) How high was the cliff?
(ii) What was the car’s velocity just before it hit the
ground ?
Tutorial questions page 31/32 Qu 1 to 3
Purple book Ex 1.4
Extra question
satellite
Example
A basket ball player throws the ball at 600 to the horizontal
with an initial speed of 5 ms-1
(a) Calculate the initial horizontal and vertical
components of velocity.
(b) The maximum height of the ball above its initial
position.
(c) The horizontal range.
Tutorial page 32 to 35 Qu 4 to 12
Purple book Ex 1.5
Estimate your take off velocity in a standing long jump.
Step 1
Vertical jump
Measure maximum vertical displacement, sv
Calculate initial vertical velocity, uv and then the
time for jump, t.
Step 2
standing long jump
sh maximum horizontal distance
assume you stay in the air for the same length of
time as your vertical jump ie uv and t will be the same as step 1.
Calculate the horizontal velocity, vH
Step 3
calculate take off velocity from uv and uH
Do you think the assumption in step 2 is justified?
If not, is the calculated value for horizontal velocity too big or too
small?
The world record for the standing long jump is 3.71 m