A 145g baseball is thrown with a speed of 25m/s . How much work was done on the baseball to reach this speed if it started from rest.

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justaguide's profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

A 145 g baseball is thrown with a speed of 25 m/s. When the thrower picks up the ball it is at rest. When it leaves the hand of the person that is throwing the ball it has a speed of 25 m/s. An object with a mass m and moving with a velocity v has a kinetic energy given by K.E. = (1/2)*m*v^2

Initially the ball is at rest and has a kinetic energy equal to 0. When it leaves the thrower's hand it has a speed of 25 m/s. Its kinetic energy when moving at 25 m/s is equal to (1/2)*0.145*25^2 = 45.3125 J This addition in energy is the work done by the thrower on the ball.

The work done by the thrower on the ball to throw it with a speed of 25 m/s is equal to 45.3125 J

norcy's profile pic

norcy | High School Teacher | (Level 1) Adjunct Educator

Posted on

The work done is the difference in the kinetic energy from the moment just prior to the baseball being thrown, that is at rest, and when it reached the speed of 25 m/s.

Kinetic energy is 1/2 x mass x V^2

The formula for Work is:

Work = 1/2 m (V2^2 – V1^2 )

= 0.5(0.145)(25^2-0^2)

= 45.3 Joules

Note: a Joule is a unit for work and is the same as a

Kg . m^2 / s^2

(I guess the squared units need ^)

pranitingale's profile pic

pranitingale | Student, Grade 9 | (Level 1) Valedictorian

Posted on

TOTAL WORK DONE = CHANGE IN KINETIC ENERGY

WORK DONE = FINAL KINETIC ENERGY - INITIAL KINETIC ENERGY

          W = (1/2)mv^2 - (1/2)mu^2

          W = (1/2)*0.145*25^2 - (1/2)*0.145*0^2

          W = 45.31 J

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