Summary

• Energy
• Definition of Work
• Vector dot (scalar) product

• Still more about work
• work by varying forces
Example #1



• Springs
• Hooke's Law applet
  I have not yet found an HTML5 equivalent to this applet.
• work to stretch a spring
Example #2
Example #3




• Kinetic energy
• derivation
• work-KE theorem W_ext = ΔK
Example #4
Example #5

PoP5 6.25
A force F = (4xi + 3yj) N acts on an object as it moves in the x direction from the origin to x = 5.00 m. Find the work done by the force on the object.
A. 50.0 J
B. 20.0 J
C. 16.0 J
D. 0.80 J
Answer



















PoP5 6.17
When a 4.00-kg object is hung vertically on a light spring, it stretches 2.50 cm. If the object is removed, how much work must an external agent do to stretch the same spring 4.00 cm from its unstretched position?
A. 1.25 J
B. 15.0 J
C. 31.4 J
D. 1568 J
Answer



















pop4 6.17
If it takes 4.00 J of work to stretch a spring 10.0 cm from its unstressed length, how much extra work is required to stretch it another 10.0 cm?
A. 6.00 J
B. 12.0 J
C. 24.0 J
D. 32.0 J
Answer



















SB5 7.30
A man does 5000 J of work to push a 2500-kg car a distance 25.0 m horizontally from rest. Neglecting friction, what is the final speed of the car?
A. 1.0 m/s
B. 2.0 m/s
C. 2.5 m/s
D. 4.0 m/s
Answer



















PoP5 6.31
What is the total work done on a 3.00-kg object as it changes its velocity from (6.00i − 1.00j) m/s to (8.00i + 4.00j) m/s? Notice that .
A. −9.00 J
B. 9.00 J
C. 55.5 J
D. 64.5 J
Answer







































answer

A. 50.0 J




















answer

A. 1.25 J




















answer

B. 12.0 J




















answer

B. 2.0 m/s




















answer

D. 64.5 J