March 4th, 2017, 01:30 PM  #1 
Member Joined: Sep 2016 From: zambia Posts: 31 Thanks: 0  work, energy and power
A 50 g pendulum bob hanging at rest on a 2 m long string is hit by a horizontal projectile of mass 80 mg moving at 200 km/h. Use the concept of energy conservation to estimate the angular displacement of the bob 
March 4th, 2017, 01:54 PM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,751 Thanks: 1401 
What kind of collision? Elastic, totally inelastic, ... ?

March 5th, 2017, 02:00 PM  #3 
Member Joined: Sep 2016 From: zambia Posts: 31 Thanks: 0 
The type of collision hasn't been specified, but I assume it's elastic.
Last edited by skipjack; March 5th, 2017 at 02:28 PM. 
March 5th, 2017, 02:07 PM  #4 
Math Team Joined: Jul 2011 From: Texas Posts: 2,751 Thanks: 1401  So, describe the physics properties of an elastic collision ...
Last edited by skipjack; March 5th, 2017 at 02:29 PM. 
March 5th, 2017, 02:16 PM  #5 
Member Joined: Sep 2016 From: zambia Posts: 31 Thanks: 0 
The kinetic energy in an elastic collision is conserved.
Last edited by skipjack; March 5th, 2017 at 02:29 PM. 
March 5th, 2017, 02:30 PM  #6 
Global Moderator Joined: Dec 2006 Posts: 18,965 Thanks: 1606  
March 5th, 2017, 02:57 PM  #7 
Math Team Joined: Jul 2011 From: Texas Posts: 2,751 Thanks: 1401  ... and momentum is conserved. $mv_{1_0}+ Mv_{2_0} = mv_{1_f}+ Mv_{2_f}$ since $M$ is initially at rest ... $mv_{1_0} = mv_{1_f}+ Mv_{2_f}$ a shortcut for conservation of kinetic energy ... closing speed of the masses prior to the collision = opening speed of the masses after the collision $\implies v_{1_0}  v_{2_0} = v_{2_f}  v_{1_f}$. Of course, $v_{2_0} = 0$. Using this equation, solve for $v_{1_f}$ in terms of $v_{2_f}$ and $v_{1_0}$. Substitute the result into the momentum equation and solve for $v_{2_f}$. Once you have $v_{2_f}$, you can use energy conservation to determine how high the pendulum bob, $M$, swings ... some trig will get you the max angular displacement from equilibrium. 

Tags 
energy, power, work 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Work,Energy and Power  jeho  Physics  3  February 22nd, 2017 04:42 PM 
Work and power problem.  Mr Davis 97  Physics  3  April 11th, 2015 05:04 PM 
Work/Energy Problem  Physicsrapper  Physics  2  December 17th, 2014 02:00 AM 
Electrical Energy and power  rsoy  Physics  1  December 24th, 2010 11:59 PM 
work and energy  izseekzu  Calculus  1  February 5th, 2010 08:37 AM 