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# s's science

### test mod. 9

Question | Answer |
---|---|

Define Reference Point | A point against which position |

Define Vector quantity | A physical measurement that contains directional information |

Define Scalar quantity | A physical measurement that does not contain directional information |

Define Acceleration | The time rate of change of an object's velocity |

Define free fall | The motion of an object when it is falling solely under the influence of gravity |

Why must one use a reference point to determine whether or not an object is in motion? | For motion to occur, object's position must change. To determine position, must be a reference point. That point allows you to determine whether position changes. Note: the statement "all motion is relative" is worth 1/2 extra point. |

After a visit to your grandmother's house, you get in your car to go home. You are in the front passenger's seat and your mother is driving. As you back out of her driveway, she stands outside waving goodbye.a. Who is in motion relative to you? | Grandmother. She is staying still, but her position relative to you is changing. |

b. Who is motionless relative to you? | Mother. Her postion relative to you does not change. |

How many miles per hour does a car travel if it makes a 40 mile trip in 30 minutes? Show all work. | This problem gives us distance and time and asks for speed. There is no direction here, so we are talking about speed. Use equation 9.1 Show me and I'll check it. Can't type it. |

What is the velocity of a bicycle (in meters per second) if it travels 1 kilometer west in 4.1 minutes? Show all work. | Problem wants velocity, which is speed and direction. You will need to do conversions. Don't forget to put direction. in your ans. (meters) Do the work and I'll check it. |

You are looking in a scientist's lab notebook and find the following unlabeledf measuring (speed, velocity, distance, acceleration, or none of these.) | This is speed. |

Define Reference Point | A point against which position |

Define Vector quantity | A physical measurement that contains directional information |

Define Scalar quantity | A physical measurement that does not contain directional information |

Define Acceleration | The time rate of change of an object's velocity |

Define free fall | The motion of an object when it is falling solely under the influence of gravity |

Why must one use a reference point to determine whether or not an object is in motion? | For motion to occur, object's position must change. To determine position, must be a reference point. That point allows you to determine whether position changes. Note: the statement "all motion is relative" is worth 1/2 extra point. |

After a visit to your grandmother's house, you get in your car to go home. You are in the front passenger's seat and your mother is driving. As you back out of her driveway, she stands outside waving goodbye.a. Who is in motion relative to you? | Grandmother. She is staying still, but her position relative to you is changing. |

b. Who is motionless relative to you? | Mother. Her postion relative to you does not change. |

How many miles per hour does a car travel if it makes a 40 mile trip in 30 minutes? Show all work. | This problem gives us distance and time and asks for speed. There is no direction here, so we are talking about speed. Use equation 9.1 Show me and I'll check it. Can't type it. |

What is the velocity of a bicycle (in meters per second) if it travels 1 kilometer west in 4.1 minutes? Show all work. | Problem wants velocity, which is speed and direction. You will need to do conversions. Don't forget to put direction. in your ans. (meters) Do the work and I'll check it. |

You are looking in a scientist's lab notebook and find the following unlabeled measuring (speed, velocity, distance, acceleration, or none of these.)a. 12.1 meters per second | This has a distance unit divided by a time unity. That's speed or velocity. Since no direction is given, this is speed. |

B. 31.2 feet | The unit of feet by itself measures distance. |

c. 14 millimeters per hour to the west | This has a distance unit divided by a time unit. That's speed or velocity. Since a direction is given, it's velocity. |

d. 4.5 yards per minute2 north | This measurement has a distance unit divided by a time unit squared. That's acceleration. The direction is necessary because acc. is a vector quantity. |

Eagle swoops down to catch a rabbit. Rabbit sees the eagle and runs. Chase ensues with the rabbit running east at 5.4 meters per second and the eagle pursuing at 4.4 meters per second. What is the relative velocity ofpredator and prey? | Eagle behind bunny, but going in same direction. Get relative velocity by subtracting individual vel.'s:rel. vel. = 5.4 meters/second - 4.4 m./second = 1.0 m./second. Bunny's going faster than eagle so rel. vel. = 1.0 m./sec. away from each other. |

What is the acceleration of an object that moves with a constant velocity? | Since the velocity is not changing, the acceleration is zero. |

A skier reaches the bottom of a slope with a velocity of 12 meters per second north. If the skier comes to a complete stop in 3 seconds, what was her acceleration? | The initial velocity is 12 meters per sec. north, and the final vel. is 0. The time is 3 sec. This is a straightforward application of equation (9.2) The neg. tells us the the acc. is in the opp. dir. of vel. Acc. is 4 m./second2 south. |

A car goes from 0--60 mph north in 5 seconds. What's the car's acceleration? | We are given time, initial velocity and final vel. Convert so time units are in agreement. Then use acc. equation. Car speeds up so acc. is in same dir. as vel. Ans. is 43,165 miles/hour2 north. (May be slight variation in how you rounded your numbers |

Person on a bridge over a river holds a rock and ball, 1 in each hand. Throws ball down towards river as hard as he can and at the same time simply drops the rock. After both have left the guy's hand, does 1 have a greater acc.? If so, which one? | Neither. Both objects are falling near the surface of the earth;so they are each in free fall. They have equal acc. Ball got more initial vel., so it will go faster, but acc. on both is the same. |

Why does a dropped feather hit the ground later than a rock dropped at the same time? | The feather is more affected by air resistance than the rock. (same as experiment 9.2). |

A physics student climbs a tree. To measure how high she has climbed, she drops a rock and times its fall. It takes 1.3 seconds for it to hit the ground. How many feet has she climbed? | Rock is in free fall so use equation 9.3. Use 32 feet per second2 as acc.Do the problem and let me check it. Cannot be typed out., 27.04 feet. |

Created by:
debra short