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Energy - PowerPoint PPT Presentation


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Energy. A crane lowers a steel girder into place at a construction site. The girder moves with constant speed. Consider the work W g done by gravity and the work W T done by the tension in the cable. Which of the following is correct?. W g is positive and W T is positive.

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slide2

A crane lowers a steel girder into place at a construction site. The girder moves with constant speed. Consider the work Wg done by gravity and the work WT done by the tension in the cable. Which of the following is correct?

  • Wg is positive and WT is positive.
  • Wg is negative and WT is negative.
  • Wg is positive and WT is negative.
  • Wg and WT are both zero.
  • Wg is negative and WT is positive.
slide3

A crane lowers a steel girder into place at a construction site. The girder moves with constant speed. Consider the work Wg done by gravity and the work WT done by the tension in the cable. Which of the following is correct?

  • Wg is positive and WT is positive.
  • Wg is negative and WT is negative.
  • Wg is positive and WT is negative.
  • Wg and WT are both zero.
  • Wg is negative and WT is positive.

The tension force is opposite the direction of motion while the gravitational force is in the same direction as the motion. The cos(theta) term in the work formula is negative.

slide4

Which force does the most work?

  • The 6 N force.
  • The 8 N force.
  • The 10 N force.
  • They all do the same amount of work.
slide5

Which force does the most work?

  • The 6 N force.
  • The 8 N force.
  • The 10 N force.
  • They all do the same amount of work.
slide6

Rank in order, from largest to smallest, the gravitational potential energies of balls 1 to 4.

  • (Ug)1 > (Ug)2 > (Ug)3 > (Ug)4
  • (Ug)4 > (Ug)3 > (Ug)2 > (Ug)1
  • (Ug)1 > (Ug)2 = (Ug)4 > (Ug)3
  • (Ug)3 > (Ug)2 = (Ug)4 > (Ug)1
  • (Ug)4 = (Ug)2 > (Ug)3 > (Ug)1
slide7

Rank in order, from largest to smallest, the gravitational potential energies of balls 1 to 4.

  • (Ug)1 > (Ug)2 > (Ug)3 > (Ug)4
  • (Ug)4 > (Ug)3 > (Ug)2 > (Ug)1
  • (Ug)1 > (Ug)2 = (Ug)4 > (Ug)3
  • (Ug)3 > (Ug)2 = (Ug)4 > (Ug)1
  • (Ug)4 = (Ug)2 > (Ug)3 > (Ug)1

Use the formula U = mgy

slide8

A small child slides down the four frictionless slides A–D. Each has the same height. Rank in order, from largest to smallest, her speeds vA tovD at the bottom.

  • vA = vB = vC = vD
  • vD > vA = vB > vC
  • vD > vA > vB > vC
  • vC > vA = vB > vD
  • vC > vB > vA > vD
slide9

A small child slides down the four frictionless slides A–D. Each has the same height. Rank in order, from largest to smallest, her speeds vA tovD at the bottom.

  • vA = vB = vC = vD
  • vD > vA = vB > vC
  • vD > vA > vB > vC
  • vC > vA = vB > vD
  • vC > vB > vA > vD
slide10

A spring-loaded gun shoots a plastic ball with a speed of 4 m/s. If the spring is compressed twice as far, the ball’s speed will be

  • 16 m/s.
  • 8 m/s.
  • 4 m/s.
  • 2 m/s.
  • 1 m/s.
slide11

A spring-loaded gun shoots a plastic ball with a speed of 4 m/s. If the spring is compressed twice as far, the ball’s speed will be

  • 16 m/s.
  • 8 m/s.
  • 4 m/s.
  • 2 m/s.
  • 1 m/s.
slide12

Four students run up the stairs in the time shown. Rank in order, from largest to smallest, their power outputs Pa to Pd.

  • Pb > Pa = Pc > Pd
  • Pd > Pa = Pb > Pc
  • Pd > Pb > Pa > Pc
  • Pb > Pa > Pc > Pd
  • Pc > Pb = Pa > Pd
slide13

Four students run up the stairs in the time shown. Rank in order, from largest to smallest, their power outputs Pa to Pd.

  • Pb > Pa = Pc > Pd
  • Pd > Pa = Pb > Pc
  • Pd > Pb > Pa > Pc
  • Pb > Pa > Pc > Pd
  • Pc > Pb = Pa > Pd