A projectile is launched upward at an angle of 70⁰ from the horizontal and strikes the ground a certain distance down range. For what angle of launch at the same speed would this projectile land just as far away?

Answer:20°

Explanation:

Recall

Range R of a projectile is given by U^2sin2A/g

We're U = velocity, A = angle of projection and g is acceleration due to gravity

From the question the range R are the same

Hence R1=R2

U1^2sin2A/g=U2^2sin2B/g

But U1=U2 and g=g

Hence sin2A=sin 2B

Sin 2*70 = sin2*B

0.6427=sin2B

B=sin inverse (0.6427) = 40/2=20°