Question

A cannon and a target are 5.1 km apart located on the same level. Find the time to hit the target. Speed of cannot is 240 ms^-1. Assume no air drag.

• A. 24.6 s, 42.6 s
• B. 24.69s, 48 s
• C. 23 s, 46.1s
• D. 21s, 41 s

Answer 1

Answer: (A)

24.6 s, 42.6 s

Answer 2

5.1 = u²sin2θ/g or

sin 2θ = $\frac{5100 \times 9.8}{240 \times 240}$

= $\frac{170}{192} = 0.88$

2θ = 61⁰42' or θ = 30⁰51'

T = $\frac{2u\sin\theta}{g} = \frac{2 \times 240 \times (1/2)}{9.8}$

= 24.69 or T = $\frac{240 \times \left( \sqrt{3/2} \right)}{9.8} = 42.6s$.