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A golf ball is launched at an angle of 20°to the horizontal, with a speed of 60m/sand a rotation rate of 90rads. Neglecting air drag, determine the number of revolutions the ball makes by the time it reaches maximum height.

Short Answer

Expert verified

The number of revolutions the ball makes when at maximum height is30

Step by step solution

01

Given

  1. Angle of launch is20°
  2. Horizontal speed is60m/s
  3. Rotational rate is90radsec
02

Understanding the concept

Find time to reach the maximum height using the kinematic equation. Using this time, find the angle in radians. The angle is nothing but angular displacement, which can be converted into a number of rotations using the relationship between one rotation and angle traced during one rotation.

Formula:

vfy=v0y+at

θ-θ0=Ӭ0t

03

Calculate the number of revolutions the ball makes by the time it reaches maximum height

Time to reach maximum height is as follows:

vfy=v0y+at

At maximum height, the velocity is zero, so

0=60sin20-9.8t⇒t=2.094sec

Now, the number of revolutions:

θ-θ0=Ӭ0t⇒θ-θ0=90×2.094⇒θ-θ0=188rad

So

188×1rev2π=29.93rev

So, the number of revolutions is 30.

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