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Chapter 9: Q. 3 (page 227)
A mother has four times the mass of her young son. Both are running with the same kinetic energy. What is the ratio vson /vmother of their speeds?
The ratio of speed is vson /vmother = 2:1
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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 particle moving to the left is slowed by a force pushing to the right. Is the work done on the particle positive or negative? Or is there not enough information to tell? Explain.
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鈥檚 kinetic energy?
Hooke鈥檚 law describes an ideal spring. Many real springs are better described by the restoring force , where q is a constant.
Consider a spring with .
It is also.
a. How much work must you do to compress this spring ? Note that, by Newton鈥檚 third law, the work you do on the spring is the negative of the work done by the spring.
b. By what percent has the cubic term increased the work over what would be needed to compress an ideal spring? Hint: Let the spring lie along the s-axis with the equilibrium position of the end of the spring at .
Then 鈭唖 = s.
Two identical horizontal springs are attached to opposite sides of a box that sits on a frictionless table. The outer ends of the springs are clamped while the springs are at their equilibrium lengths. Then a force applied to the box, parallel to the springs, compresses one spring by while stretching the other by the same amount. What is the spring constant of the springs?
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