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A box is sliding down an incline tilted at an angle 14. 0° above horizontal. The box is sliding down the incline at a speed of 1. 70 m/s. The coefficient of kinetic friction between the box and the incline is 0. 380. How far does the box slide down the incline before coming to rest?.

User Wurlitzer
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1 Answer

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The net forces on the box acting parallel and perpendicular to the incline, respectively, are

∑ F[para] = mg sin(14.0°) - F[friction] = ma

∑ F[perp] = F[normal] - mg cos(14.0°) = 0

where m = mass of the box and a = its acceleration.

The second equation tells us

F[normal] = mg cos(14.0°)

so that friction has a magnitude of

F[friction] = 0.380 F[normal] = 0.380 mg cos(14.0°)

Solve the first equation for a :

mg sin(14.0°) - 0.380 mg cos(14.0°) = ma

a = g sin(14.0°) - 0.380 g cos(14.0°)

a ≈ -1.24 m/s²

Assuming the box slides down the incline with constant acceleration, solve for ∆x, the distance it slides before coming to rest:

0² - (1.70 m/s)² = 2a ∆x

∆x = -(1.70 m/s)² / (2 (-1.24 m/s²))

∆x ≈ 1.16 m

User Doc Roms
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