(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A child operating a radio-controlled model car on a dock accidentally steers it off the edge. The car's displacement 0.77 s after leaving the dock has a magnitude of 7.4 m. What is the car's speed at the instant it drives off the edge of the dock?

@t = .77s displacement is 7.4m

a = -9.8m/s^2

2. Relevant equations

1. v_f^2 = v_i^2 + 2ad

or

2. d = v_i * t + (a * t^2)/2

3. The attempt at a solution

v_f = 7.4/.77 = 9.61m/s

1. 9.61^2 = v_i^2 + 2 * -9.8 * 7.4

... v_i = 13.38m/s, incorrect (aware of incorrectly mixing x and y components)

2. 7.4 = v_i * .77 - (9.8 * .77^2)/2

... v_i = 13.38m/s, incorrect (aware of incorrectly mixing x and y components)

3. Making a right triangle by finding v_f of an initially stationary object falling for .77s:

at + v_i = v_f

-9.8 * .77 = v_f

v_f = -7.55m/s

9.61^2 = 7.55^2 + b^2

b = 5.95

so v_i = 5.95m/s, incorrect

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# Homework Help: Finding initial velocity of a free-falling object that launched off a cliff

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