Solving exercises on pages 32, 33, 34 in Physics 8 - Atmospheric Pressure

Solve Exercise C1 on page 32 of Physics 8 Textbook

Problem Statement:

By extracting air from a paper-wrapped milk box, observe the box crumpling in various directions (H.9.2).

Explain why.

Solution:

When removing air from the milk box, the air pressure inside becomes lower than the atmospheric pressure outside. As a result, the box undergoes deformation due to the external air pressure.

Solve problem C2 on page 32 of Physics 8 textbook

Problem:

Insert a glass tube into water, seal the upper end with your finger, and then pull the tube out of the water.

Does water flow out of the tube? Why or why not?

Solution:

Water doesn't flow out of the tube because the air pressure acting on the water from below is greater than the weight of the water column.

Solve problem C3 on page 32 of Physics 8 textbook

Problem:

What happens if you remove your finger from the top of the tube? Explain why.

Solution:

When removing the finger from the tube's opening, the pressure acting on the water column equals the atmospheric pressure. At this point, the air pressure inside the tube, combined with the pressure from the water column, becomes greater than the atmospheric pressure at the tube's opening below, causing water to flow down.

Solve problem C4 on page 33 of Physics 8 textbook

Problem:

In 1654, Gerich (1602 - 1678), the Mayor of Mach - stride city in Germany, conducted the following experiment (H.9.4):

He took two hollow copper spheres, approximately 30cm in diameter, with smooth edges, and tightly pressed them together to prevent air from entering. Then, he used a vacuum pump to extract air from inside one sphere and sealed the valve. Even with eight horses pulling on each side, the spheres could not be separated.

Explain why.

Solution:

When all the air is pumped out of the sphere, the pressure inside becomes zero. Meanwhile, the sphere's surface is subjected to atmospheric pressure from all sides, tightly pressing the two spheres together. Therefore, even with eight horses per team, the spheres cannot be pulled apart.

Solve problem C5 on page 34 of Physics 8 textbook

Problem:

Are the pressures acting on A (outside the tube) and on B (inside the tube) equal? Why?

Solution:

Observing that points A and B lie on the same horizontal plane on the liquid's surface, we conclude that the pressures acting on A (outside the tube) and on B (inside the tube) are equal.

Solve problem C6 on page 34 of Physics 8 textbook

Problem:

What is the pressure acting on A? What is the pressure acting on B?

Solution:

The pressure acting on A is atmospheric pressure, and the pressure acting on B (inside the tube) is the pressure caused by the weight of a mercury column, which is 76cm high.

Solve problem C7 on page 34 of Physics 8 textbook

Problem:

Calculate the pressure at B, knowing the density of mercury (Hg) is 136,000 N/m3. Determine the magnitude of atmospheric pressure based on this.

Solution:

We have: 76cm = 0.76 m.

The pressure exerted by the weight of the 76cm high mercury column on B is:

p = d.h = 136,000 * 0.76 = 103,360 N/m2

=> The atmospheric pressure is 103,360 N/m2 (because the atmospheric pressure acting on A is equal to the pressure caused by the weight of the 76cm high mercury column inside the tube).

Solve problem C8 on page 34 of Physics 8 textbook

Problem:

Explain the phenomenon mentioned at the beginning of the problem.

'When overturning a fully-filled glass sealed with a water-impermeable paper (H.9.1), does water flow out? Why?'

Solution:

Due to atmospheric pressure acting on the paper being greater than the liquid pressure of water inside the glass on the paper, water does not flow out.

Solve problem C9 on page 34 of Physics 8 textbook

Problem:

Give an example demonstrating the existence of atmospheric pressure

Solution:

- Bend one end of a syringe needle; the medicine does not flow out. Bend both ends, and the medicine flows out easily.

- On the cap of a water bottle, a small hole allows the air pressure inside the bottle to equalize with atmospheric pressure, pushing the water down.

- Inflate a balloon, and when it's untied, it deflates.

Solve problem C10 on page 34 of Physics 8 textbook

Problem:

What does atmospheric pressure equal to 76cmHg mean? Calculate this pressure in N/m2.

Solution:

Stating that atmospheric pressure is 76 cmHg means the air exerts a pressure equal to the pressure at the bottom of a mercury column 76 cm high.

Atmospheric pressure is: p = d.h = 136,000 * 0.76 = 103,360 N/m2

Solve problem C11 on page 34 of Physics 8 textbook

Problem:

In Torricelli's experiment, assuming water instead of mercury is used, how high would the water column be? What is the minimum length required for Torricelli's tube if water is used?

Solution:

Solve problem C12 on page 34 of Physics 8 textbook

Problem:

Why can't atmospheric pressure be directly calculated using the formula p = d.h?

Solution:

To determine atmospheric pressure using the formula p = d.h, we would need to know the density and height of the atmosphere. However, the exact height of the atmospheric column cannot be accurately determined. Additionally, the density of the atmosphere varies with altitude, making it impossible to directly calculate atmospheric pressure using the formula p = d.h.

Frictional force is a crucial lesson in Chapter I of Mechanics. Check the hints for solving exercises on pages 21, 22, 23 in Physics 8 to better grasp the knowledge.

Buoyant force, the next topic in Chapter I of Mechanics in Physics 8 Grade 11. Explore the suggested solutions for exercises on pages 36, 37, 38 to strengthen your understanding and excel in Physics 8.