Which of the following expressions gives the work done by kinetic friction when a…

PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

Which of the following expressions gives the work

W_f

done by kinetic friction when a block of mass

m

slides down a rough incline, starting from rest at a vertical height

h

and reaching the bottom with speed

v

? (Take

g

as the acceleration due to gravity.) (a)

W_f = -m g h

(b)

W_f = m g h - \dfrac12 m v^2

(c)

W_f = \dfrac12 m v^2 - m g h

(d)

W_f = -\left(\dfrac12 m v^2 + m g h\right)