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 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 15th 2008, 03:40 PM #1 Junior Member   Join Date: Aug 2008 Location: United States Posts: 24 Question A few questions that I need urgent help on. Explanations for each question will be greatly appreciated! 1) A honeybee leaves the hive and travels 2 km before returning. Is the displacement for the trip the same as the distance traveled? If not, why not? 2) Two buses depart from Chicago, one going to New York and one to San Francisco. Each bus travels at a speed of 30 m /s. Do they have equal velocities? Explain. 3) Is the average speed of a vehicle a vector or a scalar quantity? Provide a reason for your answer. 4) Often, traffic lights are timed so that if you travel at a certain constant speed, you can avoid all red lights. Discuss how the timing of the lights is determined, considering that the distance between them varies from one light to the next. 5) One of the following statements is incorrect. (a) The car traveled around the track at a constant velocity. (b) The car traveled around the track at a constant speed. Which statement is incorrect and why? 6) Give an example from your own experience in which the velocity of an object is zero for just an instant of time, but its acceleration is not zero. 7) At a given instant of time, a car and a truck are traveling side by side in adjacent lanes of a highway. The car has a greater velocity than the truck. Does the car necessarily have a greater acceleration? Explain.
Sep 15th 2008, 04:04 PM   #2
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 1) A honeybee leaves the hive and travels 2 km before returning. Is the displacement for the trip the same as the distance traveled? If not, why not?
The definition of displacement (if I recall well) is the distance between the position at start and at finish. So in that case the bee returned from where it was, so the total displacement is 0, which differs from the total distance traveled.
 3) Is the average speed of a vehicle a vector or a scalar quantity? Provide a reason for your answer.
It's a scalar. Take a look at the definition of the average acceleration. According to wikipedia it's $\displaystyle \mathbf{\bar{a}}=\frac{\mathbf{v}(t+\Delta t)-\mathbf{v}(t)}{\Delta t}$ so as you can see there is no vector.
 5) One of the following statements is incorrect. (a) The car traveled around the track at a constant velocity. (b) The car traveled around the track at a constant speed. Which statement is incorrect and why?
Velocity is a vector while the absolute value of speed is its scalar. So here we have that the direction of the car changes with time (it describe a circular motion) but not the magnitude of the velocity. So the correct answer is b.

 6) Give an example from your own experience in which the velocity of an object is zero for just an instant of time, but its acceleration is not zero.
When I pitch any object in the air, when it reaches its maximum height.

 7) At a given instant of time, a car and a truck are traveling side by side in adjacent lanes of a highway. The car has a greater velocity than the truck. Does the car necessarily have a greater acceleration? Explain.
The answer is no. I give an example : the truck could be accelerating while the car (with a constant greater speed than the speed of the truck. That means the car as an acceleration equal to $\displaystyle 0$.) just pass the truck.
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 Sep 15th 2008, 04:35 PM #3 Junior Member   Join Date: Aug 2008 Location: United States Posts: 24 Thank you very much !

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a honeybee leaves the hive and travels 2 km before returning.WHAT IS THE MAGNITUDE OF THE DISPLACEMENT VECTOR OF THE BEE?

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