- #1

red123

- 22

- 0

## Homework Statement

The crate has a mass of 80 kg and is being towed by a chain which is always directed at 20º from the horizontal has shown. Determine the crate's acceleration in

*t*= 2 s if the coefficient of static friction is

*μ*

_{s}= 0.4, the coefficient of kinetic friction is

*μ*

_{k}= 0.3, and the towing force is

*P*= (90

*t*

^{2}) N, where

*t*is in seconds.

## Homework Equations

Σ

**F**=

*m*

**a**

## The Attempt at a Solution

Σ

**F**

_{x}=

*m*

**a**

_{x}

*P*cos(20º) -

*μ*

_{k}

*m*

__g__=

*m*

**a**

84.57

*t*

^{2}- 235.44 = (80 kg)

**a**

solving for

**a**when

*t*= 2

**a**= 1.29 m/s

^{2}

The answer at the back of my book is

**a**= 1.75 m/s

^{2}. I think I'm supposed to consider that static friction force is greater than kinetic friction force, but I can't figure out how to do that.