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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 2.0 kg book is lying on a 0.75-m-high table. You pick it up and place it on a bookshelf 2.25 m above the floor.
a. How much work does gravity do on the book?
b. How much work does your hand do on the book?
The cable of a crane is lifting a kg girder. The girder increases its speed from m/s to m/s in a distance of m.
a. How much work is done by gravity?
b. How much work is done by tension?
A weather rocket generates a thrust of The rocket, pointing upward, is clamped to the top of a vertical spring. The bottom of the spring, whose spring constant is , is anchored to the ground.
a. Initially, before the engine is ignited, the rocket sits at rest on top of the spring. How much is the spring compressed?
b. After the engine is ignited, what is the rocket’s speed when the spring has stretched
A uniform solid bar with mass m and length L rotates with angular velocity v about an axle at one end of the bar. What is the bar’s kinetic energy?
The left end of a spring is attached to a wall. When Bob pulls on the right end with a 200 N force, he stretches the spring by 20 cm. The same spring is then used for a tug-of-war between Bob and Carlos. Each pulls on his end of the spring with a 200 N force.
How far does the spring stretch? Explain.
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