- #1

rwishka

- 16

- 0

## Homework Statement

1. A couch with a mass of 1x10^2 kg is placed on an adjustable ramp connected to a truck. As one end of the ramp is raised, the couch begins to move downward. If the couch slides down the ramp with an acceleration of 0.70 m/s^2 when the ramp angle is 25 degrees, what is the coefficient of kinetic friction between the ramp and couch? (g = 9.81 m/s^2)

A. 0.47

B. 0.42

C. 0.39

D. 0.12

2. A crate is carried in a pickup truck traveling horizontally at 15.0 m/s. The truck applies the brakes for distance at 28.7 m while stopping with uniform acceleration. What is the coefficient of static friction between the crate and the truck bed, if the crate does not slide?

A. 0.400

B. 0.365

C. 0.892

D. 0.656

## Homework Equations

1. F = ma

u(kinetic) = Force(kinetic)/Force(normal) = Force(kinetic)/(mg)

2. Either v(final) = v(initial) + a(t)

OR

distance = 0.5(initial velocity + final velocity)(t)

OR

distance = v(inital)(t) + 0.5a(t)^2

-I think those are the three formulas I have for constant uniform acceleration. How do I choose which one to use? And what to do after finding the acceleration?

## The Attempt at a Solution

1. F=ma

F = (1 x 10^2 kg)(0.70 m/s^2)

F = 70 N

Is this right? How I involve the angle?

2. vf = vi + at

-15 = 430.5a

a = -0.0348

How can you find normal force? I know it's (mg), but is there another way? I bad at drawing diagrams, and working it out.

Please help!