Physics Problem?

2015-01-20 6:39 pm
A baseball is given an initial velocity with magnitude v0 at an angle ϕ above the surface of an incline, which is in turn inclined at an angle θ above the horizontal

Calculate the distance, measured along the incline, from the launch point to where the baseball strikes the incline. Your answer will be in terms of v0, g, θ, and ϕ.

What angle ϕ gives the maximum range, measured along the incline?

回答 (1)

2015-01-21 8:16 pm
✔ 最佳答案
I'll try the trajectory equation here: y = h + x·tanΦ - g·x² / (2v²·cos²Φ)
where y = height at x value of interest; here y = xtanΘ
and h = 0 m (assuming the ball is launched from the base of the incline)
and x = range value of interest = ???
and v = initial velocity = v0
and Φ = launch angle = Θ + φ
and Θ = angle of incline
and φ = angle of throw w/r/t incline

xtanΘ = 0 + xtan(Θ+φ) - gx² / (2(v0)²cos²(Θ+φ) → x cancels
tan(Θ+φ) - tanΘ = gx / (2(v0)²cos²(Θ+φ))
x = 2(v0)²cos²(Θ+φ)(tan(Θ+φ) - tanΘ) / g

The distance measured along the incline is
d = x / tanΘ = 2(v0)²cos²(Θ+φ)(tan(Θ+φ) - tanΘ) / gtanΘ
d = (2(v0)² / gtanΘ) * cos²(Θ+φ)(tan(Θ+φ) - tanΘ) ◄ distance

For the rest, I'll try using wolfram:
dd/dφ = 0 = secΘcos(Θ + 2φ)

I intepret the results to be
φ = π/4 - Θ/2 for the angles in radians, and
φ = 45º - Θ/2 for the angles in degrees.
Looks reasonable, I guess.

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