Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 4 - Kinematics in Two Dimensions - Exercises and Problems - Page 115: 83

Answer

$59.44\;\rm m$, $-10.82\;\rm m$

Work Step by Step

We need to make the touching velocity just at the same angle as the ramp which means it must be 20$^\circ$ below the horizontal, as you see in the figure below. Now we know that the horizontal velocity component is constant, which means that $$v_x=v_0=40{\;\rm m/s}=\dfrac{\Delta x}{t}$$ Thus, $$\Delta x=40t\tag 1$$ We know that $a_y=-g$, so $$ \Delta y=v_{0y}y-\frac{1}{2}gt^2= 0-4.9t^2$$ $$\Delta y=-4.9t^2\tag 2$$ We know that $\tan (-20^\circ)=\dfrac{v_y}{v_x}$ Thus, $$\tan (-20^\circ)=\dfrac{v_y}{v_x}=\dfrac{v_y}{40}$$ Thus, $$v_y=40\tan (-20^\circ)=-14.56\;\rm m/s$$ Now we can find $t$ by using the formula of $$v_{y}=v_{0y}+a_yt$$ Plugging the known; $$-14.56=0-9.8t$$ $$t=1.486\;\rm s$$ Plugging into (1) and (2); $$\Delta x=40\cdot 1.486=\color{red}{\bf59.44}\;\rm m$$ $$\Delta y=-4.9\cdot 1.486^2=\color{red}{\bf -10.82}\;\rm m$$
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