# English Version HSC 1st Paper 8th Chapter Physics Note

English Version HSC 1st Paper 8th Chapter Physics Note. Periodic Motion. The physics is one of the oldest academic disciplines, perhaps the oldest through the inclusion of astronomy. In the last two millennia, physics was a part of natural philosophy, chemistry, certain branches of mathematics and biology, but during the scientific revolution in the 17th century, the natural sciences emerged as unique in its own right research programs. Physics intersects with many interdisciplinary areas of research, such as Biophysics and quantum chemistry, and physics limits are not rigidly defined. New ideas in physics often explain the fundamentals of other sciences mechanisms, to open new avenues of research in areas such as mathematics and philosophy. ## English Version HSC 1st Paper 8th Chapter Physics Note

Periodic Motion

Question No. 1

A simple pendulum is taken to a hill. It completes 11990 full oscillations in 10 hours. But in-plane field, it completes an oscillation in 3 seconds. The average radius of the earth is 6400km and the height of Mount Everest is 8.854 km. (The gravitational acceleration is 9.8ms-2)

a. What is stress? 1

b. Explain the reason behind the water rise in Capillary tube made of glass. 2

c. What is the effective length of a simple pendulum? 3

d. Compare the height of the hill with respect to Mount Everest mathematically. 4

The answer to the question no. 1

a. When a body is subjected to a deforming force, a restoring force occurs in the body which is equal in magnitude but opposite in direction to the applied force. This restoring force per unit area is known as stress.

b Adhesive force between molecules of water and glass is greater than the cohesive force between molecules of water. That’s why water wets glass. Hence contact angle between water and glass is an acute one. As a result, when a capillary tube is inserted into water, the upper surface of water inside the tube become concave & surface area increases. But due to the surface tension of water, the surface tends to reduce its area which in tum produces an upward force that moves up the water inside the capillary tube.

c. Given,

at earth’s surface, period, T = 3 s

Gravitational acceleration, g = 9.8 ms-2

The effective length of the pendulum, L =?

T=2.234132 m (Ans.)

Question No. 2

A group of students in a physics laboratory hang an object of 500gm mass in a wire and swing it. They observed that it was oscillating at rate 5 per second. The displacement of the object is 5cm and the amplitude is 10 cm.

a. What is standard intensity? 1

b. The intensity of hearing of human is 1012 – Explain. 2

c. What would be the velocity of the object during the displacement in the stem? 3

d. The force during the displacement of the object in the stem would be 0.05 times to its weight- give your opinion with mathematical expressions. 4

The answer to the question no. 2

a. Standard intensity is 10-12 Wm-2 intensity of a sound of 1000 Hz frequency.

b. The least intensity of a sound that we can hear is 10-12 Wm-2.  The most intensity of a sound that’s tolerable for our car is 1Wm-2 approximately. So, the ratio between two boundaries of sound intensity for human hearing is about 1012. That means we can hear the faintest of sounds up to sounds having intensity 1012 times of it.

c.  Given, frequency, f= 0.5 Hz. Amplitude, A = 10 cm = 0.1 m. Velocity at x = 5 cm = 0.05 m Displacement, v = ?

v= 0.272 m/s (Ans.)

d. Here, mass of the bob, m = 500 g = 0.5 kg. Let’s assume, the force acting on the bob at the displacement of x = 0.05 m is F.

F= ma

or, F = max ( Considering magnitude only]

.: Force = 0.05 x Weight

So, the comment that the force acting on the bob due to the displacement of 0.05 m is 0.05 times of its weight is correct.

Question No 3.

The effective length of a second pendulum is 1m in place A and 0.9m in place B. The radius of the bob is 0.75cm.

a. Define force constant. 1

b. Pendulum watch runs slow in summer -explain why. 2

c. Calculate the angular velocity of bob in A 3

d. If an object is taken from A to B place, what will be

the change in weight? Justify your opinion with mathematical expressions.

The answer to the question no. 3

a. Force constant is the restoring force exerted by spring due to the unit displacement of its free end.

b. Period of seconds pendulum increases due to the increase of the effective length of the pendulum in summer. Hence, pendulum clock seems to run slower in summer. From the equation of period of a simple pendulum, increasing effective length, L would increase period, T as gravitational acceleration is constant in a certain place. That’s why pendulum runs slower in summer.  Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Over the last two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the scientific revolution in the 17th century, these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in academic disciplines such as mathematics and philosophy.

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