Final answer:
With a blocked pitot tube, the airspeed indicator will not provide accurate readings as it depends on the pressure difference measured by the tube. The pressure in the tube is proportional to the square of the airspeed, hence it does not linearly scale with changes in speed at the same altitude.
Step-by-step explanation:
If you have a blocked pitot tube, the pressure reading of your instrument will not accurately reflect the speed of the aircraft. A pitot tube works by measuring the difference between the static pressure and the dynamic pressure, which is the pressure of the moving air. If the tube is blocked, it may fail to measure the dynamic pressure, leading to inaccurate readings on the airspeed indicator which relies on this pressure difference to operate correctly.
As for the relationship between pressure readings and speed changes at the same altitude, assuming a simplified scenario, the pressure in the pitot tube increases with the square of the airspeed. Therefore, if the pressure reading at 200 km/h is 15.0 mm Hg, it does not linearly scale up with an increase in speed to 700 km/h. The relationship between speed and pressure is given by Bernoulli's principle, where pressure is proportional to the square of the velocity. Therefore, the increase in speed will considerably increase the pressure, but the exact value requires further calculation.