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On the putting green, a golf ball travels at 1.4 m/s in a direction of 130°. The ball encounters wind blowing at 1.1 m/s in the direction of 50°. What is the true speed and direction of the ball? Round the speed to the thousandths place and direction to the nearest degree.

On the putting green, a golf ball travels at 1.4 m/s in a direction of 130°. The ball-example-1
User Montezuma
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1 Answer

26 votes
26 votes

In order to calculate the true speed and direction of the ball, let's calculate the horizontal and vertical directions of the ball speed (b) and of the wind speed (w):


\begin{gathered} b_x=b\cdot\cos(\theta)\\ \\ b_x=1.4\cdot\cos(130°)\\ \\ b_x=1.4\cdot(-0.6428)\\ \\ b_x=-0.900\text{ m/s}\\ \\ \\ \\ b_y=b\cdot\sin(\theta)\\ \\ b_y=1.4\operatorname{\cdot}\sin(130°)\\ \\ b_y=1.4\operatorname{\cdot}0.766\\ \\ b_y=1.072\text{ m/s} \end{gathered}
\begin{gathered} w_x=w\cdot\cos(\theta)\\ \\ w_x=1.1\operatorname{\cdot}\cos(50°)\\ \\ w_x=1.1\operatorname{\cdot}0.6428\\ \\ w_x=0.707\text{ m/s}\\ \\ \\ \\ w_y=w\operatorname{\cdot}\sin(\theta)\\ \\ w_y=1.1\operatorname{\cdot}\sin(50°)\\ \\ w_y=1.1\operatorname{\cdot}0.766\\ \\ w_y=0.843\text{ m/s} \end{gathered}

Now, let's add the horizontal components together and the vertical components together:


\begin{gathered} v_x=b_x+w_x=-0.9+0.707=-0.193\text{ m/s}\\ \\ v_y=b_y+w_y=1.072+0.843=1.915\text{ m/s} \end{gathered}

To calculate the magnitude and direction of this resultant speed, we can use the formulas below:


\begin{gathered} v=√(v_x^2+v_y^2)\\ \\ v=√((-0.193)^2+(1.915)^2)\\ \\ v=1.925\text{ m/s}\\ \\ \\ \\ \theta=\tan^(-1)((v_y)/(v_x))\\ \\ \theta=\tan^(-1)((1.925)/(-0.193))\\ \\ \theta=96° \end{gathered}

Therefore the correct option is the second one.

User Pejman
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