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ANNOUNCEMENTS

ANNOUNCEMENTS Group tutoring 6:30 pm Mondays with Marit Puusepp, and 6:30 pm Thursdays with Cole Marolf. Class cancelled Fri 05 November 2010. 1 of 3.

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ANNOUNCEMENTS

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  1. ANNOUNCEMENTS • Group tutoring 6:30 pm Mondays with Marit Puusepp, and 6:30 pm Thursdays with Cole Marolf. • Class cancelled Fri 05 November 2010.

  2. 1 of 3 A balloon is dropped a distance of 100 m. Atmospheric drag is significant, causing the balloon to fall at constant speed. Through its flight the balloon lost 1 J of gravitational potential energy (DPEg = -1 J). The amount of kinetic energy gained (DKE) by the balloon is: 1 J. Zero. -1 J. y 100 v = const 0 2

  3. 2 of 3 A rocket powered launch vehicle (such as this Ares V heavy lift concept vehicle) blasts off from ground level. During the first 10 seconds of its launch, it accelerates uniformly upward and gains 1 GJ of PEg. During that same time, the vehicle: Loses 1 GJ of KE. Neither loses nor gains KE. Gains KE. y a 0 3

  4. 3 of 3 A ball drops from rest from 1 m of altitude, bounces, then reaches a maximum final altitude of 0.5 m. It had 10 J of PEg initially, but only 5 J of PEg finally. The work done on the ball by the normal force of the rigid surface was –5 J. More than –5 J but less than zero. Zero. 5 J. 4

  5. ANNOUNCEMENTS • Group tutoring 6:30 pm Mondays with Marit Puusepp, and 6:30 pm Thursdays with Cole Marolf. • Class cancelled Fri 05 November 2010.

  6. Non-conservative Forces and the General Work – Energy Theorem The work done by a non-conservative (NC) force depends upon the path of motion. Therefore, when NC forces are involved, the total mechanical energy cannot be conserved. Rather, it can be dissipated or created. ROCKET THRUST AIR DRAG Fthrust Fdrag a mg mg 6

  7. Failure of the Work – Energy Theorem • There are cases whereby the mechanical energy of a system cannot be fully accounted for (even taking into consideration the work of NC forces). • Two blobs of clay of equal mass and opposite velocity colliding and sticking together. • Two freight cars of equal mass and opposite velocity colliding and coupling. In these cases the WNC is ZERO. From the particle dynamics view, a direct transformation from mechanical energy E to thermal energy U has occurred. To find the dissipative forces responsible, one must peer into the internal structure of the bodies. 7

  8. 1 of 3 A balloon is dropped a distance of 100 m. Atmospheric drag is significant, causing the balloon to fall at constant speed. Through its flight the balloon lost 1 J of gravitational potential energy (DPEg = -1 J). The amount of kinetic energy gained (DKE) by the balloon is: 1 J. Zero. -1 J. y 100 v = const 0 8

  9. 2 of 3 A rocket powered launch vehicle (such as this Ares V heavy lift concept vehicle) blasts off from ground level. During the first 10 seconds of its launch, it accelerates uniformly upward and gains 1 GJ of PEg. During that same time, the vehicle: Loses 1 GJ of KE. Neither loses nor gains KE. Gains KE. y a 0 9

  10. 3 of 3 A ball drops from rest from 1 m of altitude, bounces, then reaches a maximum final altitude of 0.5 m. It had 10 J of PEg initially, but only 5 J of PEg finally. The work done on the ball by the normal force of the rigid surface was –5 J. More than –5 J but less than zero. Zero. 5 J. 10

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