**Example 5:** A 100-lb. block is in contact with an inclined plane as shown. Assuming the pulley is frictionless and that the coefficient of static friction between the block and the surface is 0.3, determine:

b. the maximum value of W to keep the block stationary.

Free-Body Diagram of Weight |

Free-Body Diagram (Part a) |

Free-Body Diagram (Part b) |

**Solution:**

**Part a:**

Equilibrium Equations:

(1) | |

(2) |

From Eqn. (2), N=50 lb, and from Eqn. (1), T=71.6 lb.

Therefore, W_{min}=71.6 lb to prevent the block from sliding down.

**Part b:**

Equilibrium Equations:

(3) | |

(4) |

From Eqn. (4), N=50 lb, and from Eqn. (3), T=101.60 lb.

Therefore, W_{max}=101.60 lb to prevent the block from sliding up.