Question

A van accelerates down a hill (see figure below), going from rest to 30.0 m/s in 6.30 s. During the acceleration, a toy m = 0.490 kg) hangs by a string from the van's ceiling. The acceleration is such that the string remains perpendicular to the ceiling. (a) Determine the angle e. (b) Determine the tension in the string. +-/2 points SerCP10 4.P.039. My Notes + Ask Your Teacher A dockworker loading crates on a ship finds that a 21-kg crate, initially at rest on a horizontal surface, requires a 70-N horizontal force to set it in motion. However, after the crate is in motion, a horizontal force of 55 N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between crate and floor. static friction kinetic friction

Answer 1

Given, = 0.490kg = 30mls, st = sec., m Visomis: cal we knowo, accelerations ☆ a= (30-0= * = 47-76 mols? nogle from figure, sino = no de los tres - 6.3 - - ma 0 = sin(0.485) = 29:02 (6) from figure, coso in T=mg coso = (0:49) (9:81) cos(29.02°) ... T = 402N :.(a) 0 = 29.02° (6) T = 2 •

moving Given, m = 21 kg when block is on the verge of static friction , (fs)max = Mgn. For equilibriom, Efx = 0 Fon-(fs) max=0 70 (fs)max = 70 N. AN fs - Lfs Imax - 70 is us = 70 2017 9.8 mo Now, after motion starts , the exists kinetic friction NOW, E Fx = 55-fk-0 fk = 55 N 55 o = 0.267 .., lk = 55_ 21 x 9.8 :: Ms - static friction = 0.34 elk = kinetic friction = 0.27