ADDITIONAL PROBLEMS Question 4.4a: The 1.70-kg block of wood shown in the figure

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ADDITIONAL PROBLEMS Question 4.4a: The 1.70-kg block of wood shown in the figure is pushed into a painted wall with a force of magnitude P such that the block slides vertically down the wall at a constant speed. The force is directed perpendicular to the wal and the coefficient of kinetic friction between the wood and the wall is -0.235 Determine the magnitude Pof the pushing force Question 4.4b: A 345-kg block is sliding down a ramp incined at an angle ?. 345° above the horizontal, as shown in the figure. The coefficient of kinetic friction between the block and the ramp is x 0255. Determine the magnitude of the block's acceleration down the ramp. Question 4.4c The figure shows a box of mass m 205 kg on a surface inclined at an angle of 8-23.5 The coefficient of static friction between the box and the surface is -066 The box is connected to a hanging object of mass m by a lightweight cord passing over a pulley Both the box and the hanging object are at rest. Determine the maximum possible value of m kg Need Help? Resd

Explanation / Answer

4.4a: in vertical,

F_net = f - m g = 0

f = m g

and in horizontal, F_net = N - P = 0

f = uk N

m g = u P

(1.70 x 9.8) = (0.235)(P)

P = 70.9 N  

4.4b:

N = m g cos34.5

fk = uk N = uk m g cos34.5

along the incline,

F_net = m g sin34.5 - uk m g cos34.5 =m a

a = 9.8 ( sin34.5 - 0.255 cos34.5)

a = 3.5 m/s^2

4.4 c:  

on m1:  

F_net = T - m1 g sin23.5 - fs = 0

fs_max = us N = us m1 g cos23.5

so T = m1 g sin23.5 + us m1 g cos23.5

T = (2.05 x 9.8)(sin23.5 + 0.660 cos23.5)

T = 2.05 x 9.8 N

and for m2:

F_net = T - m2 g =0

2.05 g = m2 a

m2 = 2.05 kg .....Ans

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