Class Management Help Homework - Chapter 7 Begin Date: 8/29/2017 12:00:00 AM - D
ID: 1789440 • Letter: C
Question
Class Management Help Homework - Chapter 7 Begin Date: 8/29/2017 12:00:00 AM - Due Date: 10/25/2017 11:59:00 PM End Date: 12/21/2017 12:00:00 AM (11%) Problem 9: The speed of a brick traveling on a horizontal frictional surface changes from vi = 14 m/s to vf= 12 m/s in a distance of d= 8.5 m 33% Part (a) How long in seconds did it take for the brick to slow by this amount, assuming the acceleration is constant? Grade Summary 0% 100% Potential sin() | cos() | tan() | | ( | ) | 7 | 8 | 9 Attempts remaining: 10 % per attempt) detailed view atan) acotansinh) cosh)tanh) cotanh0 1 2 3 0 END oDegrees Radians CLEAR Submit Hint I give up! Hints: 1 % deduction per hint. Hints remaining: 3 Feedback: 0% deduction per feedback. 33% Part (b) If the brick has a mass of 1 kg, what is the power supplied to the brick by friction? L 33% Part (c) What is the coefficient of kinetic friction between the brick and surface Me?Explanation / Answer
(A) Applying vf^2 - vi^2 = 2 a d
12^2 - 14^2 = 2(8.5)(a)
a = - 3.06 m./s^2
vf = vi + a t
12 = 14 - 3.06 t
t = 0.654 sec
(B) Work done = change in KE
= 1 (12^2 - 14^2) / 2
= - 26 J
P = 26 / 0.654 = 39.8 W
(C) a = - uk g
uk = 3.06 / 9.81 = 0.31