An object thatâ€™s moving with constant speed travels once around a circular path. True statements about this motion include which of the following?

(I) |
The displacement is zero. |

(II) |
The average speed is zero. |

(III) |
The acceleration is zero. |

(A) |
I only |

(B) |
I and II only |

(C) |
I and III only |

(D) |
III only |

(E) |
II and III only |

Correct Answer: A

Explanation:

Traveling once around a circular path means that the final position coincides with the initial position. Therefore, the displacement is zero. The average speed, which is total distance traveled divided by elapsed time, cannot be zero. And since the velocity changed (because its direction changed), there was a nonzero acceleration. Therefore, only I is true.