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Mechanical Energy

  • Thread starter norcal
  • Start date
  • #1
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Homework Statement



A 1.50 kg snowball is fired from a cliff 12.5 m high with an initial velocity of 14.0 m/s, directed 41.0° BELOW the horizontal. Using energy techniques ONLY, find the speed of the snowball as it reaches the ground below the cliff.

Homework Equations



(1/2)mv^2+mgy=(1/2)mv^2+mgy
Kb+Ub=Kt+Ut

The Attempt at a Solution



I am not sure how to use the angle provided with either of these equations. Is there another equation that I could use?
 

Answers and Replies

  • #2
hage567
Homework Helper
1,509
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I don't think you need anything else. You could always solve it using the equations of projectile motion to see if you get the same answer.
 
  • #3
5,428
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If you just dropped the projectile you could easily work out its final speed because you have the height, and you know the acceleration of gravity. Firing it downward will just add some vertical velocity to the drop velocity.
 
  • #4
19
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As stated in the question I am supposed to "USE ENERGY TECHNIQUES ONLY", meaning KE and U to find the velocity but I am not sure how to do this differently here than projectile motion.
 
  • #5
340
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The angle is irrelevant for the energy approach. Choose an initial and final point for you system. Are there external forces on your system-> if not then mechanical energy is conserved. Also, where are you setting potential energy to be zero?
 

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