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A 10 kg object is dropped from the same height as a 20 kg. Compare the time they take to hit the ground. |
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Object Thrown Horizontally
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How many velocities?
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2 velocities
Horizontal velocity - Determined by thrower
Vertical velocity - ??????
acceleration due to gravity
b. Objects propelled horizontally
- have 2 velocities Vx, Vy
- Vx is determined by thrower
- Vx constant (neglect fricition)
- Viy = 0 (initial vert. vel.)
- Vy changed by ........
force of gravity
Ex) Object thrown horizontally a velocity of 4 m/s
|
time (sec) |
Vx (m/s) |
Vy (m/s) |
| 0 | 4 | 0 |
| 1 | 4 | 10 |
| 2 | 4 | 20 |
| 3 | 4 | 30 |
Object dropped/Objects thrown horizontally
Same:
a) ay (+10 m/s2 )
b) vertical drop - dy
c) time in air
d) same Vy
Compare each sphere's:
A) height above the ground,
B) time in the air
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Compare the time it takes for the marbles to hit the ground.
Dropped/Projected
Horizontally
Rutgers U
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Ex1) A rock is thrown horizontally from the top of a cliff @ 150 m/s.
a) How long does it take the rock to fall 45 m vertically.
Step 1 - Underline
Ex1) A rock is thrown horizontally from the top of a cliff @ 150 m/s.
a) How long does it take the rock to fall 45 m vertically.
Step 2 - Turn information into letters
(Don't mix y information with x information)
| Horizontal | Vertical |
| Vx = 150 m/s | Viy
= 0
(thrown horizontally) |
| t = ? | ay=+9.8 m/s2 |
| dy = 45 m | |
| t = ? |
Step 3 - Substitute and Solve
∆dy = Viyt + 1/2ayt2
45 m = 0 + ˝(9.8 m/s2)t2
45 m = 4.9t2
9 = t2
t = 3 seconds
A rock is thrown horizontally from the top of a cliff @ 150 m/s
b) Find the rock's vertical velocity at 45 meters
| Horizontal Info | Vertical Info |
| Vx = 150 m/s | Viy
= 0
(thrown horizontally) |
| ay=+9.8 m/s2 | |
| dy = 45 m | |
| Vfy = ? |
Vfy2 = Viy2 + 2ad
Vfy2 = 02 + 2(+9.8 m/s2)45m
Vfy2 = 19.6(45)
Vfy = 30 m/s
Only X Equation
** dx = Vxt **
(from Vx = dx/t)
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|
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dx - Horizontal distance
Vx - horizontal velocity
ORIGINAL QUESTION
Ex1) A rock is thrown horizontally from the top of a cliff @ 150m/s. How long does it take the rock to fall 45 m vertically
c) What was the rocks' horizontal displacement after 3.0 seconds?
| Horizontal | Vertical |
| Vx = 150 m/s | Viy
= 0
(thrown horizontally) |
| t = 3.0 sec | ay = 9.8 m/s2 |
| dx = ? | dy = 45 m |
| t = 3.0 sec |
Given
Vx = 150 m/s
(Object thrown horizontally)
dx = ?
(A.K.A. Range)
t = 3.0 seconds
** dx = Vxt **
d
x = 150 m/s(3.0 seconds)
= 450 m
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Projectile Fired Horizontally 2 |
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