Question

A ball of mass 0.5 kg slows down from a speed of 5 ms-1 to that of 3 ms-1.Calculate the change in the kinetic energy of the ball.

Answer 1

Answer:

Change in KE = 4m/s

Explanation: We have the formula ; KE  = $\frac{1}{2}$mv^2

First case : Ball moving with the speed of (v) = 5 m/s

KE (1) = 1/2 *m* v^2 -------- (a)

Second case : Ball slows down with the speed of (v')= 3 m/s

KE(2) = 1/2 * m * v' ^2 ------- (b)

Therefore, change in KE i.e.  [ a - b ]

KE(1) - KE(2) = [1/2 * m * v^2] - [  1/2 * m * v' ^1 ]

                   = 1/2 *m * [ v^2 - v'^2 ]

                   = 1 / 2 * 0.5 * [ 25 - 9 ]

                   = 4 m/s   ans .

         

Answer 2

Answer:

Explanation:

Change in Kinetic Energy =0.5m(vf^2-vi^2)

where m is mass of ball, vf is final speed and vi is initial speed.

 

we have vf = 3 m/s   and vi = 5 m/s

 

Change in Kinetic Energy = (1/2)×0.5×(32 - 52) = -4 J

hence Kinetic energy decreases by 4 J