Solve Kinematics: Find Vi of Flea Jumping 0.390m

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To find the initial velocity (Vi) of a flea jumping to a maximum height of 0.390m, the equation vf^2 = vi^2 + 2ad is used, where vf is the final velocity at the peak (0 m/s), a is the acceleration due to gravity (-9.8 m/s²), and d is the height (0.390 m). The negative sign in acceleration indicates that gravity opposes the flea's upward jump. By rearranging the equation, the issue of negative velocity can be resolved by recognizing the directional nature of the vectors involved. Ultimately, the correct application of the kinematic equation allows for the calculation of Vi without confusion over sign conventions.
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A flea jmps to a maximum height of 0.390m. Find vi as it leaves the ground.

I thought of using the equation vf^2 = vi^2 + 2ad
but in this case, if i want to find out vi, I get
-vi^2 = 2ad.
and because of the negative, it doesn't work...

How do you solve this problem??
 
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jnimagine said:
A flea jmps to a maximum height of 0.390m. Find vi as it leaves the ground.

I thought of using the equation vf^2 = vi^2 + 2ad
but in this case, if i want to find out vi, I get
-vi^2 = 2ad.
and because of the negative, it doesn't work...

How do you solve this problem??

Acceleration due to gravity: a = -9.8m/s2 note the minus sign!

The reason why this is negative: the flea is jumping up (positive direction), acceleration is acting down (negative direction as it is opposite to the direction of the jump)

This cancels out your problem of negative displacement when you realize you are working with vectors that have different directions.
 

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