Question

In the absence of air resistance, at what other angle will a thrown ball go the same distance as one thrown at an angle of 75 degrees? A. 15 degrees. B. 65 degrees. C. 70 degrees. D. 80 degrees. E. 90 degrees.

Answer 1

As we know that range of the projectile motion is given by

$R = \frac{v^2 sin(2\theta)}{g}$

here we know that range will be same for two different angles

so here we can say the two angle must be complementary angles

so the two angles must be

$\theta, 90 - \theta$

so it is given that one of the projection angle is 75 degree

so other angle for same range must be 90 - 75 = 15 degree

so other projection angle must be 15 degree