Finding the Initial Speed of a Blue Car in a Projectile Motion Scenario

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SUMMARY

The discussion focuses on calculating the initial speed of a blue car involved in a projectile motion scenario after colliding with a stationary red car. Key parameters include a reaction time of 2/3 seconds, a skid distance of 60 meters, a coefficient of friction of 0.75, and a height of 1.47 meters for the blue car. The acceleration due to gravity is given as 9.8 m/s², and the angle of the hill is 2 degrees. The participant has successfully calculated the final velocity of the pizza sign in the y-direction as 5.36 m/s but seeks further assistance in determining the car's initial velocity.

PREREQUISITES
  • Understanding of projectile motion principles
  • Familiarity with kinematic equations, specifically Vf² = Vi² + 2a * deltaX
  • Knowledge of friction coefficients and their impact on motion
  • Basic skills in vector decomposition for analyzing motion in two dimensions
NEXT STEPS
  • Calculate the time it takes for the pizza sign to hit the ground using kinematic equations
  • Determine the initial velocity of the blue car using the relationship between the sign's motion and the car's speed
  • Explore the effects of friction on braking distance and stopping time
  • Review concepts of energy conservation in collision scenarios
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the dynamics of collisions and projectile motion in real-world scenarios.

Joel M
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Homework Statement


A blue car carrying a pizza sign goes over a hill and sees a red car stopped at the bottom. The blue car is unable to stop in time and hits the red car, sending the pizza sign flying.

The blue car's reaction time is 2/3 of a second.
The length of the skid marks from the point which the blue car started braking to the point where it hit the red car is 60m.
The sign traveled 11m before hitting the ground.
The coefficient of friction between the blue car's tires and the ground is .75.
The height of the car is 1.47m.
The angle of the hill is 2 degrees.
Find the car's initial speed.

(Assume that the cars crashed on a level surface, assume the red car did not move, and assume that the pizza sign was not mounted on the car. Acceleration of gravity is 9.8m/s^2. Disregard air resistance.)

Homework Equations


Vf^2 = Vi^2 * 2a * deltaX?
I'm sure there is more, but I first need to figure out where to start.

The Attempt at a Solution


I drew up this diagram in photoshop and uploaded it to flickr:
4074346500_5535009bd5_o.jpg


I decided to first find the time that it takes for the sign to hit the ground. I then broke up the signs properties into x and y components. I used the equation listed above to find final velocity in the y direction which came out to be 5.36m/s. I am now stuck. I'm not even sure that I started it correctly. Any help from here would be greatly appreciated!
 
Last edited:
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The pizza sign is a clue to how fast the car was traveling when it hit the red car. Therefore you need to find its initial velocity.
 
That's what I am trying to do. Once I get further I will update this thread. Thanks.
 

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