Please help projectile motion problem #2

  • Thread starter phys1618
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  • #1
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Please help!! projectile motion problem #2

Homework Statement


A girl throws a rock straight out form the roof of a building. the rock has a velocity of 25 m/s when it leaves the girl's hand, and the rock hits the ground 3 seconds later.
1. how far from the bas e of the building does the rock land?
2. how tall is the building?
3. with what velocity does teh rock hit the ground?
4. how far from the top of the builidng does the rock land?



Homework Equations



d=vit + (1/2)at2
c2= a2 + b2
tan theta= opp/adj
a=(vf-vi)/t

The Attempt at a Solution



I'm unsure if my answers are correct. however, I tried and this is what i got
1. 75m
2. 45m
3. 39.05 m/s at 50.19o below ground
4. 87.46m (this is the one I'm really unsure about)

all help and inputs are greatly appreciated. thank you for your time and efforts.
 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,097
5


Homework Statement


A girl throws a rock straight out form the roof of a building. the rock has a velocity of 25 m/s when it leaves the girl's hand, and the rock hits the ground 3 seconds later.
1. how far from the bas e of the building does the rock land?
2. how tall is the building?
3. with what velocity does teh rock hit the ground?
4. how far from the top of the builidng does the rock land?



Homework Equations



d=vit + (1/2)at2
c2= a2 + b2
tan theta= opp/adj
a=(vf-vi)/t

The Attempt at a Solution



I'm unsure if my answers are correct. however, I tried and this is what i got
1. 75m
2. 45m
3. 39.05 m/s at 50.19o below ground
4. 87.46m (this is the one I'm really unsure about)

all help and inputs are greatly appreciated. thank you for your time and efforts.

For 2, if you used 10 as acceleration of gravity then that would be correct. But the more correct answer would use gravity as 9.8m/s2

I get a different answer for 3 by about 7 degrees but I think that may have to do with your treatment of part 2. I would guess your method is ok.
Part 4 is good enough for Government work.

Cheers.
 

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