Question

Two pegs A and B were fixed on opposite banks of a 40 m wide river level was set up at A and the staff readings on pegs A and B were observed as 1.250 m and 1.600 m respectively. Thereafter the Instrument was shifted and set up at B. The staff readings on pegs B and A were observed as 0.800 m and 0.250 m respectively. If the R.L of peg A is 120.450 m then the R.L (in m) of peg B is

• A. 120.00
• B. 120.05
• C. 120.20
• D. 120.15

Answer 1

The correct option is A 120.00

Staff reading shows that station B is lower than station A

$a_1=1.250m;a_2=0.250m$
$b_1=1.600m;b_2=0.800m$

$h_{AB}=\frac{(b_1-a_1)+(b_2-a_2)}{2}$

$=\frac{(1.600-1.250)+(0.800-0.250)}{2}$

= 0.450 m

$\therefore$ RL of B = RL of A - 0.450

= 120.450 - 0.450

= 120.000 m