Question

a rugby player passes the ball 5.34 m across the field, where it is caught at the same height as it left his hand. at what angle was the ball thrown if its initial speed was 7.7 m/s, assuming that the smaller of the two possible angles was used

Answer 1

Answer:

$31.035^{\circ}$

Explanation:

x = Displacement in x direction = 5.34 m

t = Time taken to travel the displacement

y = Displacement in y direction = 0

u = Initial velocity of ball = 7.7 m/s

g = Acceleration due to gravity = $9.81\ \text{m/s}^2$

Displacement in x direction is given by

$x=u\cos\theta t\\\Rightarrow t=\dfrac{5.34}{7.7 \cos\theta}$

Displacement in y direction is given by

$y=u\sin\theta t-\dfrac{1}{2}gt^2\\\Rightarrow 0=7.7\sin\theta \dfrac{5.34}{7.7\cos\theta}-\dfrac{1}{2}\times 9.81 (\dfrac{5.34}{7.7\cos\theta})^2\\\Rightarrow 0=7.7\sin\theta-4.905\times \dfrac{5.34}{7.7\cos\theta}\\\Rightarrow 0=7.7^2\sin\theta \cos\theta-4.905\times 5.34\\\Rightarrow 0=7.7^2\dfrac{\sin2\theta}{2}-4.905\times 5.34\\\Rightarrow 0=7.7^2\sin2\theta-4.905\times5.34\times 2\\\Rightarrow \sin2\theta=\dfrac{4.905\times 5.34\times 2}{7.7^2}\\\Rightarrow 2\theta=\sin^{-1}\dfrac{4.905\times 5.34\times 2}{7.7^2}$

$\Rightarrow \theta=\dfrac{62.07}{2}\\\Rightarrow \theta=31.035^{\circ}$

The angle at which the ball was thrown is $31.035^{\circ}$.