अभ्यास प्रष्न,Practice Questions | ठोंसो के यांत्रिक गुण | 11th |Physics |Chap 9|Part 5 |Sourabh sir

A Physics teacher explains the concept of relative velocity to her students in class. She emphasises that when two bodies are moving in opposite directions, their relative velocity is sum of the velocities of the two. And when two bodies are moving in the same direction, their relative velocity is difference of the velocities of the two. Students are confused. The teacher then takes two balls one red and the other green. She says suppose red ball moves with a velocity 5 m//s and green ball moves with a velocity of 4 m//s from a common point, and along the same straight line. if red ball is moving to the right and green ball is moving to the left, then after 1 sec , red ball is at R' , where R R' = 5 m and green ball is at G' where G G' = 4 m , Figure. The distance between the two balls after 1 sec = G' R' G G' + R R' = (4 + 5) = 9 m . This is the magnitude of their realtive velocity. If both the balls are moving to the right, as shown in Figure. The distance between the two balls after sec = G' R' - G G' = 5 - 4 = 1 m . In that case, relative velocity = 1m//s . (a) Read the above passage and answer the following questions : (i) What value has the Physics teacher displayed ? (ii) What have the students picked up ? (iii) Give atleast one practical example of the concept.

Read the following information carefully to answer the questions that follow. In a survey of 25 students, it was found that 15 have taken Mathematics. 12 have taken Physics and 11 taken Chemistry, 5 have taken Mathematics and Chemistry, 9 have taken Mathematics and Physics, 4 have taken Physics and Chemistry and 3 have taken all the three subjects. The number of students who have taken only Physics, is (a)2 (b)3 (c)5 (d)6

Read the following information carefully to answer the questions that follow. In a survey of 25 students, it was found that 15 have taken Mathematics. 12 have taken Physics and 11 taken Chemistry, 5 have taken Mathematics and Chemistry, 9 have taken Mathematics and Physics, 4 have taken Physics and Chemistry and 3 have taken all the three subjects. The number of students who have taken only two subjects, is (a)7 (b)8 (c)9 (d)10

The ratio of the efficiencies of A, B and C is 2 : 5 : 3. Working together, they can complete a work in 27 days. B and C together can complete 4/9th part of that work in: A, B और C की कार्य क्षमता का अनुपात 2 : 5 : 3 है | एक साथ कार्य करते हुए, वे किसी कार्य को 27 दिन में पूरा कर सकते हैं | B और C एक साथ उस कार्य के 4/9 भाग को कितने दिनों में पूरा करेंगे ?

Read the following information carefully to answer the questions that follow. In a survey of 25 students, it was found that 15 have taken Mathematics. 12 have taken Physics and 11 taken Chemistry, 5 have taken Mathematics and Chemistry, 9 have taken Mathematics and Physics, 4 have taken Physics and Chemistry and 3 have taken all the three subjects. Consider the following statements I. The number of students who have taken only one subject is equal to the number of students who have taken only two subjects. II. The number of students who have taken at least two subjects is four times the number of students who have taken all the three subjects. Which of the above statement(s) is/are correct?

A metal foil is at a certain distance from an isotropic point source that emits energy at the rate P. Let us assume the classical physics to be applicable. The incident light energy will be absorbed continuously and smoothly. The electrons present in the foil soak up the energy incident on them. For simplicity , we can assume that the energy incident on a circular path of the foil with radius 5xx10^(-11) m (about that of a typical atom ) is absorbed by a single electron. The electron absorbs sufficient energy to break through the binding forces and comes out from the foil. By knowing the work function, we can calculate the time taken by an electron to come out i.e., we can find out the time taken by photoelectric emission to start. As you will see in the following questions, the time decay comes out to be large, which is not practically observed. The time lag is very small. Apparently, the electron does not have to soak up energy . It absorbs energy all at once in a single photon electron interaction. The experimental observations show that the waiting time for emission is 10^(-8) s. This observation contradicts the calculations based on classical physics view of light energy . Thus we have to assume that during photoelectron emission