- #1
Kira
- 8
- 0
Basically my teacher hands us out a review packet for physics and says to do it if we want practice...Okay I do the packet and I have it done, now my problem is that the teacher didn't give out the answers to the problems so I have no idea whether or not I did it right...so I am hoping some one will check my work before I take my midterm tomorrow. Sorry for being so troublesome.
Anyways here are a few problems and my work involved. I don't know how to do those picture equations so bear with me
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1. The height of a helicopter above ground is given by h = 3t³, where h is in meters and t is in seconds. After 2 seconds, the helicopter releases a small mailbag, How long after its release does the mailbag reach the ground.
h = 3t³
h(2) = 24 m
h' = 9t²
v(2) = h' = (9)(2)² = 36 m/s
Si 0
Sf 24m
Vi -36 m/s
Vf 42 m/s
a 9.8 m/s²
t ?
I know that I have my signs placed oddly but that's how my brain works. Also I put all the information I have in the chart already from the work I get below except time.
Vf² = Vi² + 2a(Sf - Si)
Vf = sqrt(Vi² + 2a(Sf-Si))
Vf = sqrt((-36)² + (2)(9.8)(24))
Vf = 42 m/s
Vf = Vi + at
t = Vf-Vi/a
t = 42+36/9.8
t = 7.96 s
I think that's right but I want to make sure.
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2. A 100 g bullet is fired from a rifle having a barrel 0.6 m long. Assuming the origin is placed where the bullet begins to move, the force (in Newtons) exerted on the bullet by the expanding gas is 15000 + 10000x - 25000x², where x is in meters. Determine the work done by the gas on the bullet as the bullet travels the length of the barrel.
work:
F(x) = 15000 + 10000x - 25000x²
F(.6) = 15000 + 10000(.6) - 25000(.6)²
F(.6) = 12000 N
w = Fd
w = (12000N)(.6N) = 7200 J
Okay I think I did that problem horribly wrong because I mean its too easy and this is advanced physics.
One last problem
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A catcher "gives" with the ball when he catches a 0.15 kg baseball moving at 25 m/s. If he moves his glove a distance of 2 cm, what is the average force acating on his hand?
Work
Ke = (1/2)mv²
Ke = (1/2)(.15)(25)²
Ke = 46.87 J
Ke = (1/2)(.15)(0)² (Im assuming the ball stops)
Ke = 0 J
w = Kef - Kei
w = Fd
F = w/d
F = 46.87J/.02m = 2343.75 N
thanks for your time...I feel really bad now asking someone to check my work.
Anyways here are a few problems and my work involved. I don't know how to do those picture equations so bear with me
--------------------------
1. The height of a helicopter above ground is given by h = 3t³, where h is in meters and t is in seconds. After 2 seconds, the helicopter releases a small mailbag, How long after its release does the mailbag reach the ground.
h = 3t³
h(2) = 24 m
h' = 9t²
v(2) = h' = (9)(2)² = 36 m/s
Si 0
Sf 24m
Vi -36 m/s
Vf 42 m/s
a 9.8 m/s²
t ?
I know that I have my signs placed oddly but that's how my brain works. Also I put all the information I have in the chart already from the work I get below except time.
Vf² = Vi² + 2a(Sf - Si)
Vf = sqrt(Vi² + 2a(Sf-Si))
Vf = sqrt((-36)² + (2)(9.8)(24))
Vf = 42 m/s
Vf = Vi + at
t = Vf-Vi/a
t = 42+36/9.8
t = 7.96 s
I think that's right but I want to make sure.
-------------------------------
2. A 100 g bullet is fired from a rifle having a barrel 0.6 m long. Assuming the origin is placed where the bullet begins to move, the force (in Newtons) exerted on the bullet by the expanding gas is 15000 + 10000x - 25000x², where x is in meters. Determine the work done by the gas on the bullet as the bullet travels the length of the barrel.
work:
F(x) = 15000 + 10000x - 25000x²
F(.6) = 15000 + 10000(.6) - 25000(.6)²
F(.6) = 12000 N
w = Fd
w = (12000N)(.6N) = 7200 J
Okay I think I did that problem horribly wrong because I mean its too easy and this is advanced physics.
One last problem
----------------------------
A catcher "gives" with the ball when he catches a 0.15 kg baseball moving at 25 m/s. If he moves his glove a distance of 2 cm, what is the average force acating on his hand?
Work
Ke = (1/2)mv²
Ke = (1/2)(.15)(25)²
Ke = 46.87 J
Ke = (1/2)(.15)(0)² (Im assuming the ball stops)
Ke = 0 J
w = Kef - Kei
w = Fd
F = w/d
F = 46.87J/.02m = 2343.75 N
thanks for your time...I feel really bad now asking someone to check my work.