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Chapter 9: Q. 38 (page 228)
How much energy is consumed by
(a) a kW hair dryer used for min and
(b) a W night light left on for h?
a). Energy consumed by hairdryer J
b). Energy consumed by night lightJ
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A firefighter needs to climb the stairs of a -tall building while carrying a backpack filled with gear. How much power does he need to reach the top in ?
A -cm-long vertical spring has one end fixed on the floor. Placing a kg physics textbook on the spring compresses it to a length of cm. What is the spring constant?
A kg air compressor is dragged up a rough incline from m to m, where theaxis is vertical. How much work does gravity do on the compressor during this displacement?
A sprinter accelerates from rest. Is the work done on the sprinter positive, negative, or zero? Explain
You need to raise a heavy block by pulling it with a massless rope. You can either (a) pull the block straight up height h, or (b) pull it up a long, frictionless plane inclined at a 15 o angle until its height has increased by h. Assume you will move the block at constant speed either way. Will you do more work in case a or case b? Or is the work the same in both cases? Explain.
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