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Phys298SolnsHW1_3_4

# Phys298SolnsHW1_3_4 - SOLUTIONS FOR HW 1 3 AND 4 GRADED...

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SOLUTIONS FOR HW 1, 3, AND 4 GRADED PROBLEMS HW 1: graded problems were Ch. 2, #20 and #23 20. With an average speed equal to the highway speed limit, ! t = ! r / v = (5000 mi)/(65 mi/h) = 76.9 h after 1995, and ! t = (5000 mi)/(55 mi/h) = 90.9 h before, a difference of 14.0 h. 23. Interpret This is a one-dimensional kinematics problem involving finding the velocity as a function of time, given position as a function of time. The object of interest is the model rocket. Develop The instantaneous velocity v ( t ) can be obtained by taking the derivative of y ( t ). The derivative of a function of the form bt n can be obtained by using Equation 2.3. Evaluate (a) The instantaneous velocity is v ( t ) = dy dt = b ! 2 ct . (b) The velocity is zero when b = 2 ct , or t = b 2 c = 82 m/s 2(4.9 m/s 2 ) = 8.37 s. Assess As the model rocket is launched upward with an initial velocity b = 82 m/s, its altitude increases and then reaches a maximum, where the instantaneous velocity is zero. The rocket then falls back to the Earth.

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