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Figure8-5a shows two industrial spies sliding an initially stationary 225 kg floor safe a displacement vec(d) of magnitude 8.50 m. The push vec(F)_(1) of spy001 is 12.0 N at an angle of 30.0^(@) downward from the horizontal, the pull vec(F)_(2) of spy 002 is 10.0 N at 40.0^(@) above the horizontal. The magnitudes and directions of these forces do not change as the safe moves, and the floor and safe make frictionless contact. (b) During the displacement, what is the work W_(g) done on the safe by the gravitational force vec(F)_(g) and what is the work W_(N) done on the safe by the normal force vec(F)_(N) from the floor ? |
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Answer» Solution :KEY IDEA Because these FORCES constant in both magnitude and direction, we can find the WORK they do with EQ. 8-7. Calculations: Thus, with mg as the magnitude of the gravitational force, we write `W_(g)=mgd COS 90^(@)= mgd(0)=0` And `W_(N)=F_(N)d cos 90^(@)=F_(N)d(0)=0` We should have known this result. Because these forces are perpendicular to the displacement of the safe, they do zero work on the safe and do not transfer any ENERGY to or from it. |
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