Solve Projectile Motion: Angle=20°, Height=20m

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Homework Help Overview

The discussion revolves around a projectile motion problem involving a car moving along a slope, with a specified angle of 20 degrees and a height of 20 meters. Participants are attempting to determine the time it takes for the car to hit the ground and the initial velocity components.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants are discussing how to calculate the initial vertical and horizontal velocity components based on the given angle and speed. Questions are raised about the correct application of kinematic equations to find the time of flight and the position where the car hits the ground.

Discussion Status

There is an ongoing exploration of the kinematic equations, with some participants questioning the signs used in their calculations. Guidance has been offered regarding the correct interpretation of the coordinate system and the signs of the variables involved.

Contextual Notes

Participants are navigating potential confusion regarding the direction of acceleration and displacement, as well as the implications of their chosen coordinate system. There is an emphasis on ensuring consistency in the signs of the variables used in the equations.

dsptl
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A car is moving with constant velocity along a slope as shown in the figure. The magnitude of the velocity is 10m/s. Find the position of point A where the car hits the ground.

Angle = 20 degree
Height = 20m


http://maxupload.com


I have freaking no idea form where to start. Please help asap
 
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What is the initial velocity in the vertical and horizontal directions?
 
i think

Vy = 10sin20degree

Vx = 10cos20degree
 
Alright, now how can you determine how long before it hits the ground?
 
danago said:
Alright, now how can you determine how long before it hits the ground?

y = vi * t + .5at*t

20 = 3.4t - 5t*t
 
dsptl said:
y = vi * t + .5at*t

20 = 3.4t - 5t*t

You need to be careful of your signs. You have acceleration as negative there, but you have both displacement and velocity as positive, even though they are in the same direction as acceleration here. If you try to solve that you will get complex solutions.
 
so is it like

-20 = -3.4t - 5t*t
 
dsptl said:
i think

Vy = 10sin20degree

Vx = 10cos20degree
Is the positive y direction in your coordinate system pointing downward?
 
dsptl said:
so is it like

-20 = -3.4t - 5t*t

Thats better.
 
  • #10
then I just multiply t by Vx to get the ans

thx a lot 4 the help
 

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