Question

Give short answer to the following questions:
(i) Why sliding friction is less than static friction?
(ii) When the free ends of a tester are dipped into a salt solution, the magnetic needle shows deflection. Can you explain the reason?
(iii) A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency?
(iv) Write two musical instruments and their vibrating part producing sound.
(v) Cans of which metal is preferred over iron for storing food and why?

Answer 1

1. friction come into play when irragularities present in the surface of two object in contact get interlocked with each other. In sliding the time given for interlocking is very small . Hence interlocking is very small. Therefore less force is required to overcome this interlocking . because of this reason sliding friction is less than static friction
2. electric current produces magnetic effect which causes deflection of the magnectic needle of a compass so when the free end of a tester are dipped into a soltuion which is a good conductor of electricity the neddle show deflection .
3. frequency = no. of oscillation / time
= 40/4 = 10 Hz
time period = 1 / frequency of oscillation
= 1/10 = 0.1 sec
4. a.) sitar = string
b.) dholak = its head
5. tin cans made for storing food are made by electroplating tin onto iron

Answer 2

Answer:

1. The friction between the two surfaces is because of the interlocking of the irregularities of the two surfaces. During sliding, contact points do not get enough time to get interlocked properly. Therefore, less friction. This explains why sliding friction is less than static friction.
2. The deflection occurs because the circuit becomes complete since free ends of the tester are dipped in a solution. The solution is certainly a conducting solution. This is the reason why the compass needle shows a deflection.
3. Time period is defined as the time required to complete one oscillation.

• Frequency is defined as the number of oscillations per unit time.
• Time = 4 sec.
• Time Period = (Time taken) / (Number of Oscillations)
• Time Period = (4/40) = 0.1 sec.
• Frequency = (Number of Oscillations)/ (Time taken)Frequency = (40/4) =10H

4.Musical instrument, any device for producing a musical sound. The principal types of such instruments, classified by the method of producing sound, are percussion, stringed, keyboard, wind, and electronic.

5.Tin cans

Tin cans, used for storing food, are made by electroplating tinonto iron. Tin is less reactive thaniron. Thus, food does not come into contact with iron and is protected from getting spoilt. So, a coating of zinc is deposited on iron to protect it from corrosion and formation of rust.