Two packages at UPS start sliding down the 20?ramp shown in the figure. Package

Question

Two packages at UPS start sliding down the 20?ramp shown in the figure. Package A has a mass of 5.00kg and a coefficient of kinetic friction of 0.220. Package B has a mass of 12.0kg and a coefficient of kinetic friction of 0.170.
(Figure 1)

How long does it take package A to reach the bottom?

Could someone tell me how to do this problem? Thank you!

Two packages at UPS start sliding down the 20?ramp shown in the figure. Package A has a mass of 5.00kg and a coefficient of kinetic friction of 0.220. Package B has a mass of 12.0kg and a coefficient of kinetic friction of 0.170. (Figure 1) How long does it take package A to reach the bottom? Could someone tell me how to do this problem? Thank you!

Explanation / Answer

ma*g*sin20 - ua*ma*g*cos20 + mb*g*sin20 - ub*mb*g*cos20 = ma*a

(ma+mb)*g*sin20 - g*cos20*(ma*ua+mb*ub) = ma*a

a = 5.61 m/s^2

s = ut + 0.5*a*t^2

2 = 0.5*5.61*t^2

t = 0.84 s

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