Question

Staff reading on the floor of a verandah of school building is 1.815 m and staff reading when held with bottom of staff touching the ceiling over the verandah is 2.870 m. R.L. of the floor is 74.500 m Height of the ceiling above floor is
1. 4.270 m
2. 4.685 m
3. 3.955 m
4. 4.920 m

Answer 1

Correct Answer - Option 2 : 4.685 m

Concept:

When staff is held vertically downward, then Height of instrument is

H I = Reduce Level (RL) + Staff Reading (SR)

When Staff is held inverted then

HI = RL - SR

Height of Ceiling above floor = RL of Ceiling – RL of Floor

Calculation:

RL of Floor = 74.50 m

SR when staff held upright position is 1.815 m

Hence, HI = 74.5 + 1.815 = 76.315 m

SR when Staff held inverted = 2.870 m

In this case, HI = RL of Ceiling – SR = R L of Ceiling - 2.870

In both cases, height of instrument will not change as such location of instrument is not changed.

∴ 76.315 m = RL of ceiling – 2.870

⇒ RL of ceiling = 79.185 m

Now,

Height of Ceiling above floor = RL of Ceiling – RL of Floor

Or

Height of ceiling above floor = 79.185 – 74.50 = 4.685 m