A block of mass 10 kg , moving in x direction with a constant speed of 10 ms^(-1), is subjected to a retarding force F = 0.1 x J//m during its travel from x = 20m to 30 m. Its final KE will be

A block of mass 10 kg , moving in x direction with a constant speed of

1.	A block of mass 10 kg , moving in x direction with a constant speed of 10 ms^(-1), is subjected to a retarding force F = 0.1 x J//m during its travel from x = 20m to 30 m. Its final KE will be
Answer» 275 J 250 J 475 J 450 J Solution : Here, `10kg, v_(i)=10ms^(-1)` Initial kinetic energy of the block is `K_(i)=(1)/(2)mv_(i)^(2)=(1)/(2)xx(10kg)xx(10ms^(-1))^(@)=500J` Work done by retarding force `W=int_(x_(1))^(x_(2))F_(r)dx=int_(20)^(30)-0.1xdx=-0.1[(x^(2))/(2)]_(20)^(30)` `=-0.1[(800-400)/(2)]=-25J` According to work - energy theorem, `W=K_(f)-K_(i)` `K_(f)=W+K_(i)=-25J+500J=475J`