Ballistic bullet pendulum conservation of momentum problem

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Homework Statement


A 15 g bullet is fired into a 2.55 kg block that is hanging by a 2.0 m long string. The speed of the bullet is 425 m/s.

Calculate the angle when the system reaches its maximum height?


Homework Equations


m1v1=(m1+m2)vf

(1/2)mv^2=mgh


The Attempt at a Solution



(0.015 kg)(425 m/s) = (0.015 kg + 2.55 kg)vf
vf=2.49 m/s

(.5)(2.565 kg)(2.49 m/s)^2=(2.565)(9.8)h
h=.316 m

Now that I have my height, I am not sure what to do. I think it should be a simple trig function at this point, but I cannot get the correct answer which is 32.6 degrees. I've also tried using L-Lcosθ=h, but have not had luck with that.

Thanks in advance.
 

Answers and Replies

  • #2
ehild
Homework Helper
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Homework Statement


A 15 g bullet is fired into a 2.55 kg block that is hanging by a 2.0 m long string. The speed of the bullet is 425 m/s.

Calculate the angle when the system reaches its maximum height?


Homework Equations


m1v1=(m1+m2)vf

(1/2)mv^2=mgh


The Attempt at a Solution



(0.015 kg)(425 m/s) = (0.015 kg + 2.55 kg)vf
vf=2.49 m/s

(.5)(2.565 kg)(2.49 m/s)^2=(2.565)(9.8)h
h=.316 m

Now that I have my height, I am not sure what to do. I think it should be a simple trig function at this point, but I cannot get the correct answer which is 32.6 degrees. I've also tried using L-Lcosθ=h, but have not had luck with that.

Thanks in advance.
Your work is correct so far, and yes, use L-Lcosθ=h. What is your problem with it?


ehild
 

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