You are 2 km from the launch pad, watching a mighty rocket climb skyward, under the fearless command of the intrepid Captain Knight. Your first observation gives an angle of elevation of 21 degrees. Five seconds later, the angle increases to 35 degrees. What was the rocket’s average speed during the five-second interval?

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*x* meters |
is the speed we want. |

5 seconds |

2000 |
= cos 21 → *y* = |
2000 |
≈ 2142 m. |

*y* |
cos 21 |

*x* |
= |
*y* |
→ *x* = |
*y* sin 14 |
= |
2000 |
· |
sin 14 |
≈ 633 meters. |

sin 14 |
sin 55 |
sin 55 |
cos 21 |
sin 55 |

So the speed = |
633 |
≈ 127 m/sec. |

5 |