16. describe a cars velocity as it goes around a track at a constant speed. 17. explain why streets and…

16. describe a cars velocity as it goes around a track at a constant speed. 17. explain why streets and highways have speed limits rather than velocity limits. 18. identify for each of the following news stories, determine whether the objects speed or velocity is given: the world record for the hundred - meter dash is about 10 m/s; the wind today is 30 km/h from the north - west, a 200 000 kg train was traveling north at 70 km/h when it derailed; a car was issued a ticket for traveling at 140 km/h on the interstate. 19. think critically you are walking toward the back of a bus that is moving forward with a constant velocity. describe your motion relative to the bus and relative to a point on the ground.

16. describe a cars velocity as it goes around a track at a constant speed. 17. explain why streets and highways have speed limits rather than velocity limits. 18. identify for each of the following news stories, determine whether the objects speed or velocity is given: the world record for the hundred - meter dash is about 10 m/s; the wind today is 30 km/h from the north - west, a 200 000 kg train was traveling north at 70 km/h when it derailed; a car was issued a ticket for traveling at 140 km/h on the interstate. 19. think critically you are walking toward the back of a bus that is moving forward with a constant velocity. describe your motion relative to the bus and relative to a point on the ground.

Answer

Brief Explanations:

  1. Velocity is a vector quantity having both magnitude (speed) and direction. When a car goes around a track at a constant speed, its speed is unchanging, but its direction is constantly changing as it moves along the curved path. So, the car's velocity is not constant.
  2. Speed is a scalar quantity (just a magnitude), while velocity is a vector (magnitude and direction). It is more practical to set limits on the magnitude of motion (speed) for vehicles on streets and highways as the direction of motion can vary greatly and is harder to regulate. Also, speed limits are easier to enforce and understand for drivers.
  • The world - record for the hundred - meter dash (about 10 m/s) gives speed as it only mentions a magnitude and no direction.
  • The wind speed of 30 km/h from the northwest gives velocity as it has both magnitude (30 km/h) and direction (northwest).
  • A 200,000 kg train traveling north at 70 km/h gives velocity as it has magnitude (70 km/h) and direction (north).
  • A car issued a ticket for traveling at 140 km/h on the interstate gives speed as it only mentions the magnitude of motion.
  • Relative to the bus: Since you are walking toward the back of the bus while the bus is moving forward, your velocity relative to the bus is in the backward direction.
  • Relative to a point on the ground: Your velocity relative to the ground is the vector sum of the bus's forward - moving velocity and your backward - moving velocity relative to the bus. If the bus's forward velocity is (v_{bus}) and your backward velocity relative to the bus is (v_{you/bus}), your velocity relative to the ground (v = v_{bus}-v_{you/bus}). If (v_{bus}>v_{you/bus}), you are still moving forward relative to the ground, just at a slower speed than the bus. If (v_{bus}<v_{you/bus}), you are moving backward relative to the ground.

Answer:

  1. The car's velocity is not constant because its direction is constantly changing while its speed is constant.
  2. Speed is a scalar and easier to regulate and enforce than velocity (a vector), and direction of motion on streets/highways is variable and hard to control.
  • World - record for hundred - meter dash: Speed
  • Wind speed from northwest: Velocity
  • Train traveling north: Velocity
  • Car on interstate: Speed
  • Relative to the bus: Backward motion
  • Relative to a point on the ground: Depends on the magnitudes of your velocity relative to the bus and the bus's velocity; could be forward (if bus's forward velocity is greater) or backward (if your backward velocity relative to the bus is greater)