A golfer is being taught by a golf pro to improve his swing. In one exercise, th

Question

A golfer is being taught by a golf pro to improve his swing.   In one exercise, the pro tells him to raise his club over his head, and just let it swing down in a smooth circular motion--with no push from his arms--till the club hits the ball.   Assume the club head, which has a mass of 200 grams, swings in a semi-circle till it hits the 46 gram golf ball.   Just before it hits, the club head is traveling at a velocity of 8.4 m/s.

(A)    How high was club head before it swung down?

Now the golf pro tells him to put some effort into the same motion, and the golfer gets the club head moving at 20 m/s as it hits the ball.  
          (B) How much net work does the golfer do on the club in the course of the swing?

Explanation / Answer

(A) Applying energy conservation,

PEi + KEI = PEf + KEF

0 + m v^2 / 2 = m g h + 0

h = 8.4^2 /(2 x 9.8)

h = 3.6 m

(B) Work done = change in KE

= 0.200 (20^2 / 2 - 0)

= 40 J

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