Question

A projectile is fired at an angle of 30º to the horizontal such that the vertical component of its initial velocity is 80 m/s. Its time of flight is T. Its velocity at t = T/4 has a magnitude of nearly :

• A. 200 m/s
• B. 300 m/s
• C. 140 m/s
• D. 100 m/s

Answer 1

Answer: (C)

140 m/s

Answer 2

$\frac{u_{x}}{u_{y}}$= cot 30⁰ =$\sqrt{3}$ \ u_x =80$\sqrt{3}$ m/s

T =$\frac{2u_{y}}{g}$ \ T = 16 s

At t =$\frac{T}{4}$= 4s, v_x = 80$\sqrt{3}$ m/s

v_y = 80 – 10 × 4 = 40 m/s

\ v =$\sqrt{(80\sqrt{3})^{2} + (40)^{2}}$= 140 m/s