A technician uses a rubber suction cup to hold a warning sign against a smooth glass panel. Fig. 1 shows a cross-section through the cup. Most of the air is...
Question 1 Report
A technician uses a rubber suction cup to hold a warning sign against a smooth glass panel. Fig. 1 shows a cross-section through the cup. Most of the air is pushed out when the cup is pressed onto the glass. The area inside the circular rim is 0.0060 m². Atmospheric pressure outside the cup is 100 000 Pa and the pressure of the trapped air is 82 000 Pa.
(a) Calculate the pressure difference across the suction cup. [2]
(b) State which side of the cup has the greater pressure. [1]
(c) Explain why the suction cup is held against the glass. [3]
Answer Details
(a) The pressure difference is:
\[100000\text{ Pa}-82000\text{ Pa}=18000\text{ Pa}\]
[2]
(b) The outside, atmospheric-air side of the cup has the greater pressure. [1]
(c) Atmospheric air exerts a greater pressure on the outside of the cup than the trapped air exerts inside it. This pressure difference creates a resultant force towards the glass, holding the cup in place. The smooth rim forms a seal that prevents air entering under the cup and removing the pressure difference. [3]
Download The App On Google Playstore
Everything you need to excel in your exams
