Question

The force P is applied to the 49-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 = 219 N, and (c) P = 311 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 μs = 0.29 and μk = 0.25, respectively. The friction force is positive if up the incline, negative if down the incline.

49 kg V/ 20 4, = 0.29 M = 0.25 17° Answers: Z Z Z Z

Answer 1

Ques 49kg 120 ins (static hk (Kinetic friction coefficient) = 0.29 friction coefficient) = 0.25 @ when P=0 hores 499 SDI mati Balancing the force along inclined & Baloncing the force along t to plane. Fi ( Posce along in cline)= 'PCOS 20°- 499 Sin 17" Fs (maximum static friction = NN - Einx (49J Cos 17°-Psinzo) @ Fs) in case a = hs x (49g Cosit = 33.30N Pi=49g sin 17 (down incline) Fs) maro < 49gsinit gf means block will start on 73 spiding downward o kinetic fiction will & act along ireline in up motion direction. Fc) maxo = chKX 499 Cos 17° = 114.92 Neloton. Fik) maio 49981117= 140154 V 499 Cos17

F = Fmaxo SO IF = 114.92N © when P = 219 N Fs) maxo = vhs x (4.99 Cositº - psin 20) Fstmaxo = 111:58 N Force along inclined f. (Film = p Cos 200-49 g Sin 17 = 65.25 N Cup Incline) Sina Fs)maxo> (fi) with friction Ye. will not allow the Block to so F = fi F - 65.25 N Deer -down the incline, © P = 311 N Fs/maxo = uns X (49 g Cos17 - P Sinzo). Esmaxo = 10 2046 2 N Force along incline = P Cos 20 - 499sih 17° TFT fi= 151.704N Since Fi) Fs) mayo Block will start moring in up incline direction 8 friction force will come into the picture.

OPATE / 1201 F - Fe) more che (499c8s 17º – Ps in 20°) = 88.3294 N so F = 88·3294 N to initiate @ what value of p is required motion up the incline - to initiate motion up the incline- FS maxo = fi chs x( 499 Cos 17° psin 20) = ('p Cos 20° — 499 Sidia) 133•308 - :29XP Sin 20° - p cos 20°-1406540 PlCos 2004. 2g sin2o) = 273-808 P = 26 3056/N IP = 263-56 N / need to start the motion up incline.

When the body comes in motion kinetic friction comes in picture but in case of rest static friction comes in picture.