Finding the average velocity of a car traveling at different speeds and angles

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SUMMARY

The discussion focuses on calculating the average velocity of a car that travels east at 95 km/h for 1.5 hours and then at 111 km/h at an angle of 30° east of north for 1.8 hours. The correct approach involves using the law of cosines to find the resultant distance and then dividing by the total time to determine average velocity. The final calculations yield a magnitude of 170.23 km and an average velocity of 33.1 m/s at an angle of 32.5° north of east. Participants emphasized the importance of including units in calculations to avoid errors.

PREREQUISITES
  • Understanding of kinematics and vector addition
  • Familiarity with the law of cosines
  • Basic knowledge of trigonometric functions
  • Ability to convert units (e.g., km/h to m/s)
NEXT STEPS
  • Study the law of cosines in detail for vector calculations
  • Learn about vector decomposition and how to resolve vectors into components
  • Practice converting speeds from km/h to m/s for various scenarios
  • Explore additional kinematic equations for average velocity and acceleration
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Students studying physics, particularly those focusing on kinematics and vector analysis, as well as educators looking for examples of real-world applications of these concepts.

Intrusionv2
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Homework Statement



A car travels east at 95 km/h for 1.5 hours. It then travels 30.0° east of north at 111 km/h for 1.8 hours.

What is the average velocity for the trip? (Magnitude and degrees)

Homework Equations



law of cosines/resultant

The Attempt at a Solution



I have tried doing this:
d=952 + 1112 - 2(85*111)cos60 = 110km
v=110km / 3.3 hr = 33.1 m/s

for the angle...
tanx = Bsinx/ a + bcosx = 111sin60/95+111cos60 = 0.638
x = 32.5 north of east

Both of these were wrong...any help please??
 
Last edited:
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Intrusionv2 said:
d=852 + 1112 - 2(85*111)cos60 = 170.23km
You have basically the right idea to use the law of cosines, but this step is wrong. If you include the units in the calculation, you will see why.
 
diazona said:
You have basically the right idea to use the law of cosines, but this step is wrong. If you include the units in the calculation, you will see why.

Nvm, I see now.
 
Last edited:

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