# Engineering Mechanics

## Centripetal Force of a Ball Revolving Uniformly in a Horizontal Circle

**Problem**

A 150 g ball at the end of a string is revolving uniformly in a horizontal circle of radius 0.600 m. The ball makes 2 revolutions in a second. What is the centripetal acceleration?

A. 74.95 m/sec^{2} |
C. 49.57 m/sec^{2} |

B. 94.75 m/sec^{2} |
D. 59.47 m/sec^{2} |

## Angle Between Two Zero-Based Vectors in XY-Plane

**Problem**

What is the angle between zero-based vectors ${\bf V_1} = (-\sqrt{3}, ~ 1)$ and ${\bf V_2} = (2\sqrt{3}, ~ 2)$ in an *x*-*y* coordinate system?

A. 0° | C. 150° |

B. 180° | D. 120° |

## Y-component of Vector A if Vectors A and B are Orthogonal

**Problem**

Compute the value of *b* if **A** and **B** are orthogonal.

$${\bf A} = 2{\bf i} + b{\bf j} + {\bf k}$$

$${\bf B} = 4{\bf i} - 2{\bf j} - 2{\bf k}$$

A. 6 | C. 4 |

B. 5 | D. 3 |

## Burning Bale from Catapult to Travel 150 ft and Clear Over 35 ft Castle Wall

**Problem**

A catapult is placed 100 ft from the castle wall, which is 35 feet high. The soldier wants the burning bale of hay to clear the top of the wall and land 50 feet inside the castle wall. If the initial velocity of the bale is 70 feet per second, then at what angle should the bale of hay be launched so that it travel 150 feet and pass over the castle wall. Use *g* = 32 ft/sec^{2}.

A. 49.8° | C. 39.2° |

B. 50.8° | D. 40.2° |

## Truss With Tension-Only Diagonals

**Situation**

Diagonals *BG*, *CF*, *CH*, and *DG* of the truss shown can resist tension only.

If *W* = 3 kN and *P* = 0, find the following:

1. the force in member *CF*.

A. 4.76 kN | C. 4.67 kN |

B. 4.32 kN | D. 4.23 kN |

2. the force in member *BF*.

A. 3.2 kN | C. 3.4 kN |

B. 3.3 kN | D. 3.5 kN |

3. the force in member *DH*.

A. 2.8 kN | A. 2.5 kN |

B. 2.8 kN | D. 2.7 kN |

## 3-Panel Truss with Flexible Cables Used as Diagonals

**Situation**

Flexible cables *BE* and *CD* are used to brace the truss shown below.

1. Determine the load *W* to cause a compression force of 8.9 kN to member *BD*.

A. 7.80 kN | C. 26.70 kN |

B. 35.64 kN | D. 13.35 kN |

2. Which cable is in tension and what is the tensile reaction?

A. BE = 12.58 kN |
C. BE = 6.29 kN |

B. CD = 6.29 kN |
D. CD = 12.58 kN |

3. If *W* = 20 kN, what will be the tensile reaction of member *CE*?

A. 6.67 kN | C. 0 |

B. 13.33 kN | D. 10 kN |