1.

A ball of mass 100 gm is projected upwards with velocity 10 m/s. It returns back with 6 m/s. Findwork done by air resistance.

Answer»

W net =W mg +W air = 1 2 m(v f ^ 2 -v i ^ 2 )


Rightarrow0+W air = 1 2 *0.1[(6)^ 2 -(10)^ 2 ]=- - 3.2


From work energy thergy theorem,

Wnet=Wmg + Wair resistance

According to Work-Energy theorem,

Wnet = change in K.E.

 So, Wmg = 0 and Wair = 1/2m(vf 2 - vi 2 )

  =1/2×0.1(62 - 102 ) = -3.2 J.




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