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# If the coefficient of kinetic friction between the 150lb crate and the ground is us=0.21. Determine the speed of the crate when t=4s.?

If the coefficient of kinetic friction between the 150lb crate and the ground is us=0.21. Determine the speed of the crate when t=4s. The crate starts from rest and is towed by the 100lb force.

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- FiremanLv 72 months agoFavorite Answer
As 1 lb = 0.45 kg

=>m = 150 lb = 68 kg

=>F = 100 lb = 45 kg = 45 x 9.8 N = 441 N

Thus by F(net) = F(applied) - F(friction)

=>ma = F - μk x N

=>68 x a = 441 - 0.21 x (mg)

=>68a = 441 - 0.21 x 68 x 9.8

=>a = 4.43 m/s^2

Thus by v = u + at

=>v = 0 + 4.43 x 4

=>v = 17.71 m/s

NOTE: As there is motion instead of μ(static), it shall be μ(kinetic). Since μk is not provided in the data, μs data is utilised as μs.

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