Harold the Hurler is a physics student who is renowned for his baseball pitching

Question

Harold the Hurler is a physics student who is renowned for his baseball pitching arm. In order to determine the amount of work he performs in throwing a baseball, Harold devises an experiment. He stands at the bottom of a deep pit and hurls a 142-g baseball through an open third-floor window in a nearby building. Harold's aim is so accurate that the ball then smoothly enters the tube of the Baseball Absorber that Harold invented and patented. In this device the ball compresses a spring until it comes momentarily to rest, and this maximum amount of compression is recorded as 47.9 cm. The spring's force constant is 873 N/m, and the position of the baseball's momentary rest is 7.79 m above ground level. The point in the pit where the Hurler starts his pitch is 12.9 m below ground level. How much work does Harold perform on the baseball? Take g = 9.80 m/s^2.

Explanation / Answer

m =142g, x =47.9cm, g=9.8 m/s^2 , k = 873 N/m

h =7.79+12.9 = 20.69m

There are two types potential energies stored in base ball: potential energy in baseball and potential energy in spring

U = mgh+(1/2)kx2

U = [(0.142)(9.8)(20.69)]+[(1/2)(873)(0.479)2]

U =28.79+100.15

Total enegy when ball come to rest U = 128.94 J

If there is no friction force, then work done on base ball equal to change in potential energy

W = 128.94 J

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