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4. A 25.0-kg block is initially at rest on a horizontal surface. A horizontal force of 75.0 N is required to set the block in motion, after which a horizontal force of 60.0 N is required to keep the block moving with constant speed. Find
(a) the coefficient of static friction and
(b) the coefficient of kinetic friction between the block and the surface.
4. A 25.0-kg block is initially at rest on a horizontal surface. A horizontal force of 75.0 N is required to set the block in motion, after which a horizontal force of 60.0 N is required to keep the block moving with constant speed. Find
(a) the coefficient of static friction and
(b) the coefficient of kinetic friction between the block and the surface. `f_k = µ_kn`
`f_s = µ_sn`
(a) 0.306 (b) 0.245
Given:
`f_s = 75.0 N`
`f_k = 60 N`
`m = 25.0\ kg`
Equations:
`f_k = µ_kn`
`f_s = µ_sn`
(a)
`f_s = µ_s times n`
`mu_s = f_s / n`
`n = mg`
`mu_s = f_s/(mg) = 75.0 / (25.0 times 9.8) = 0.306`
(a)
`f_k = mu_k times n`
`mu_s = f_k / n`
`n = mg`
`mu_s = f_k/(mg) = 60.0 / (25.0 times 9.8) = 0.245`
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