7. Ballistic Pendulum H L L L L m M A projectile of mass m moving horizontally with speed v strikes a stationary mass M suspended by strings of length L . Subsequently, m + M rise to a height of H . Given H , M and m what is the initial speed v of the projectile? M + m v V V =0 See I.E. 1 in homework demo Collision Conserves Momentum 0+m v = (M+m) V After, Conserve Energy ½ (M+m) V 2 +0 = 0+(M+m) g H V = sqrt(2 g H) Combine:
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10. Explosions ACT “ before” A B Which of these is possible? (Ignore friction and gravity) A B C =both D = Neither “ after” P x = 0 and P y = 0 P x = 0, but P y > 0 P x = 0, and P y = 0 M
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12. Center of Mass Center of Mass of a system behaves in a SIMPLE way - moves like a point particle ! - velocity of CM is unaffected by collision if F ext = 0 (pork chop demo) P tot = M tot V cm F ext t = P tot = M tot V cm So if F ext = 0 then V cm is constant Also: F ext = M tot a cm
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Editor's Notes
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Define Elastic, Inelastic and totally inelastic
Lots of people think inelastic means 0 KE at end.
Transparency. Note that H = ½ L (x/L)^2 useful since we measure x not H.
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