Answer to Question #863 in Mechanics | Relativity for duha
Question #863
A projectile is fired from the top of a cliff of height h above the ocean below. The projectile is fired at an angle θ above the horizontal and with an initial speed vi.(a) Find a symbolic expression in terms of the variables vi, g, and θ for the time at which the projectile reaches its maximum height.(b) Using the result of part (a), find an expression for the maximum height hmax above the ocean attained by the projectile in terms of h, vi, g, and θ.
Expert's answer
Let's write equations of the motion
for the projection which is perpendicular to the ground:
vy=vi sin(θ);
h=h0 + v0yt - gt2/2;
vy = v0y - gt.
for the projection which is parallel to the ground:
vx=vi cos(θ);
vx=v0x.
The projectile reaches maximum height when vy = 0
v0y - gt = 0;
t = v0y / g = vi sin(θ) / g.
b) h(max) = h0 + vi sin(θ) * vi sin(θ)/g - g*(vi sin(θ)/g)2 / 2 = h0 + 1/2 (vi sin(θ)/g)2/g.
for the projection which is perpendicular to the ground:
vy=vi sin(θ);
h=h0 + v0yt - gt2/2;
vy = v0y - gt.
for the projection which is parallel to the ground:
vx=vi cos(θ);
vx=v0x.
The projectile reaches maximum height when vy = 0
v0y - gt = 0;
t = v0y / g = vi sin(θ) / g.
b) h(max) = h0 + vi sin(θ) * vi sin(θ)/g - g*(vi sin(θ)/g)2 / 2 = h0 + 1/2 (vi sin(θ)/g)2/g.
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