Final answer:
The magnitude of the projectile's horizontal velocity at the point where its velocity vector makes an angle of 50° with respect to the horizontal is vo ∙ cos 70°.
Step-by-step explanation:
The magnitude of the projectile's horizontal velocity at the point where its velocity vector makes an angle of 50° with respect to the horizontal can be found using the equation:
Vx = vo * cos θ
Where Vx is the horizontal velocity, vo is the initial velocity, and θ is the launch angle. In this case, the launch angle is 70° and the initial velocity is not given. Therefore, the magnitude of the projectile's horizontal velocity at that point is option E, vo ∙ cos 70°.