Alan is trying to throw a ball across a 50m wide river 100m below him. Alan knows physics so he throws the ball at a 45 degree upward angle at 30m/s for maximum distance. Will the ball cross the river?

Respuesta :

Answer:

yes

Explanation:

u = 30 m/s

θ = 45°

h = - 100 m (below)

d = 50 m

g = - 9.8 m/s^2

Use second equation of motion in vertical direction

[tex]h=u_{y}t +\frac{1}{2}a_{y}t^{2}[/tex]

[tex]-100=30\times Sin45\times t -0.5\times 9.8t^{2}[/tex]

[tex]-100 = 21.21 \times t -4.9 \times t^{2}[/tex]

[tex]t=\frac{21.21\pm \sqrt{21.21^{2}+4\times4.9 \times 100}}{9.8}[/tex]

By solving we get

t = 7.17 s

The horizontal distance traveled in this time

= u Cos45 x t = 30 x 0.707 x 7.17 = 152.1 m

This distance is more than the width of the river, So the ball crosses the river.