Question

The force P is applied to the 67-kg block when it is at rest. Determine the magnitude and direction of the friction force exerted by the surface on the block if (a) P = 0, (b) P 185 N, and (c) P 296 N. (d) What value of P is required to initiate motion up the incline? The static and kinetic coefficients of friction between the block and the incline are us 0.17 and u 0.14 respectively. The friction force is positive if up the incline, negative if down the incline. 67 kg 19 0.17 0.14 11 Answers (a) F= (b) F= (c) F= N (d) P=

Answer 1

Nt Psinig Peos 19 N+ Psinmga Fret Pos 19 mg sin It PEo, N=mg s Psinis N fricten favce 0.17 x 67x9.8 xCes1 paand) (dur to ngsin downwnd) 10 6 N Now, ma sin 12 5.28N g sin N meams will be active) frietion force 0.19x67x9.8x Cs -90-23 N (+) (4) F t 90-23 N

P- 185N Net up ward frePeas 19mg sinit 49.64N - 4 1-12S 28 my Cos Psin 13-(i09.6-Go22) = 19.36 frietion force stetie) >0.17 Y926 8 39 N Fret fK will be aetiva 20-14 x N 014 x 49 36 691N 6 91N P 296 N P sin 13 mg Cos1 N 2 r09. 6-9. 36 = 1 3.23 N 2 frictn forer N 014 x123 23 - 185 1.85 N

a initiate motian wenees force P Cos P stn 19 o 14 (m cos 17 (5.88t Sin 13) P109.6 109 6 - P> 6 21 17 65 N