Free Fall
Upward Motion
Free Fall Calculations
Upward Motion Calculations
100
Free fall motion is...
Falling caused by gravity, with nothing else effecting it (no air resistance)
100
An object moving upward in the air is ___________ because gravity is pulling in the opposite direction.
Slowing down!
100
An object is released from very high up. After 2 seconds how fast is it going?
v = gt v = 2s(-10m/s^2) v = -20m/s Remember the negative sign only refers to direction
100
A rock is tossed upwards at 40 m/s. How long does it take to reach its highest point?
t = v/g t = (40m/s)/(10m/s) t = 4 s OR you can subtract 10 m/s every second until you get to 0 m/s (which is the top).
200
During our lab work and demonstrations, did we use true "free fall" motion? Stick to the definition.
No! In class we always have to deal with air, which we ignore for free fall motion.
200
At the very top of upward motion, what does the object do as it changes from moving upward to moving downward?
It stops!
200
A ball is dropped from a lab table. How far will it travel in 0.3s?
d=1/2gt^2 d = 1/2(-10m/s^2)(0.3s)^2 d = -0.45m The negative means that the ball is now below where it began.
200
A rock is tossed upward with a velocity of 40 m/s. How high does it go?
t = v/g = 4s d = 1/2gt^2 + vt d = 1/2 (-10m/s^2)(4s)^2 + (40m/s)(4s) d = 80 m
300
What is the acceleration of objects free falling?
-10 m/s^2 Remember the negative means direction. Gravity points down (and is causing the acceleration) so the acceleration is negative.
300
Upward motion is symmetrical. Explain what that means.
It means: distance traveled up = distance traveled down, time to get to the top = time to get back down, speed at a given height going up = speed at same height going down
300
A physics marble falls a distance of 1.2 meters. How long did it take to hit the ground?
t = sqrt(2d/g) t = sqrt(2(-1.2m)/(-10m/s^2)) t = 0.49s
300
A bow is fired straight into the air with a velocity of 51 m/s. How long does it take to hit the ground?
time up = v/g = 51/10 = 5.1s time down = 5.1s because it is SYMMETRICAL total time is 10.2s
400
Object A has a mass of 10kg Object B has a mass of 50kg If we drop both A and B from the same height at the same time, which will hit the ground first?
They will hit the ground at the same time because the acceleration due to gravity (little g) does not change when mass changes.
400
The first half of upward motion has a positive ___________ and a negative ____________
Initial velocity, acceleration (gravity)
400
A falling pastry hits the ground with a velocity of 23 m/s. How long was it falling?
t = v/g t = (-23m/s)/(-10m/s^2) t = 2.3s
400
When a rocket is launched it has an initial velocity of 131 m/s. How fast is it going when it returns to Earth?
131 m/s because upward motion is SYMMETRICAL.
500
Object A has a mass of 10kg Object B has a mass of 50kg If both A and B roll off a table with the same speed, which will hit the ground farther from the table.
They will hit at the same distance. Because both objects A and B will fall at the same rate they will be in the air for the same amount of time. They are also going the same speed, so they will cover the same amount of distance in the time before they hit the ground.
500
Once the object has reached its peak (highest it can travel) we can consider the motion to be ____________ until it hits the ground.
Free fall
500
A falling chunk of ice smashes into the ground with a velocity of 18 m/s. How high did it fall from?
t = v/g = 1.8s d = 1/2gt^2 d = 1/2(-10m/s^2)(1.8s)^2 d = -16.2 m, this is the height the ice FELL (it is negative because it is now below where it started). The height it fell FROM is 16.2 m
500
A student bouncing on a trampoline is bounced upward at 11.3 m/s. How high does the student go? How long is the student in the air?
t = v/g = 11.3/10 = 1.13s d = 1/2 gt^2 + vt d = 1/2 (-10m/s)(1.13)^2 + (11.3 m/s)(1.13s)^2 d = 6.4m Time in air = time up + time down = 1.13s + 1.13s = 2.26s
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