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

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