A body of mass 10 kg slides down an inclined plane from rest.Its height from the ground level is 10m.The inclined plane is not smooth.When the body reaches the ground its speed is 14 m/s.Then how much work is done against friction?(g=10 m/s2)

Potential energy at the highest point= Kinetic energy at the lowest point + Work done against frictionHence,Work done against friction is,W=PE-KE    =mgh-12mv2    =10×10×10-12×10×142    =1000 -980    =20 J

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