Question

please i need his asap

A projectile is fired with an Initial velocity of 800 ft/s at a target B Neglecting air resistance, succcssful firing angle a Is closest to

Answer 1

12000 = 800 cos(a) * t

=> t = 15 / cos(a) .... (1)

_____________________

2000 = 800 sin(a) * t - 1/2 g t^2

2000 = 12000 tan(a) - 16 (225 / cos^2 (a) )

so 2000 = 12000 tan(a) - 3600 / cos^2 (a)

so 10 = 60 tan(a) - 18 / cos^2 (a)

divide by 2 , multiply by cos^2(a) you get :

5 cos^2 (a) = 30 sin(a) cos(a) - 9

=> 5cos^2(a) + 9 = 15 sin(2a)

if you solve this eqn you will get :

a = 70 degrees (check with calculator)

so option (D) is correct

Answer 2

the range of the projectile is maximum for an angle A = 45o

the range is

R = (u^2 x sin(2A)/g)

where u is initial speed of projectile and g = 9.8 m/s^2