IMathAS-libretexts

A block of mass m is pulled across a rough surface, as shown above. The coefficient of friction between the block and the surface is $\displaystyle \mu$ _k. The force F that pulls the block is exerted at the angle $\displaystyle \phi$ shown. Which of the following is an expression for the magnitude of a frictional force on the block if it is moving at a constant speed?

$\displaystyle \mu$ _k(Fsin( $\displaystyle \phi$ ) + mg)
$\displaystyle \mu$ _k(mg - Fsin( $\displaystyle \phi$ ))
$\displaystyle \mu$ _kmg
$\displaystyle \mu$ _k(Fsin( $\displaystyle \phi$ ) - mg)
$\displaystyle \mu$ _kFcos( $\displaystyle \phi$ )

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