A man walks on a straight road from his | Class 11 Physics Chapter Motion in a straight Line, Motion in a straight Line NCERT Solutions

Question:

A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km h –1. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km h–1. What is the

a) magnitude of average velocity, and

b) average speed of the man over the interval of time (i) 0 to 30 min, (ii) 0 to 50 min, (iii) 0 to 40 min?

[Note: You will appreciate from this exercise why it is better to define average speed as total path length divided by time, and not as magnitude of average velocity. You would not like to tell the tired man on his return home that his average speed was zero!]

Answer:

(i)

Time taken by the man to reach the market from home,  t1  =  2.5/5  =  ½ h = 30 min

Time taken by the man to reach home from the market, t2  = 2.5/7.5  =  1/3 h  =  20 min

Total time taken in the whole journey = 30 + 20 = 50 min

Average velocity  =  Displacement / Time  =  2.5 / ½  =  5 km/h                ..... (a(i))

Average speed   =  Distance /  time  =  2.5 / ½  =  5 km/h                ..... (b(i))

 

(ii) Time = 50 min =  5/6 h

Net displacement = 0

Total distance = 2.5 + 2.5 = 5 km

Average velocity  =  Displacement / Time  =  0             ..... (a(ii))

Average speed   =  Distance /  time  = 5 / 5/6  =  6 km/h           ..... (b(ii))

 

(iii)

Speed of the man = 7.5 km

Distance travelled in first 30 min = 2.5 km

Distance travelled by the man (from market to home) in the next 10 min 

= 7.5 x 10/60 = 1.25 km

Net displacement = 2.5 – 1.25 = 1.25 km

Total distance travelled = 2.5 + 1.25 = 3.75 km

Average Velocity  =  1.25 / 40/60  =  1.25x3 / 2  =  1.875km/h   ...........  (a(iii))

Average Speed =  3.75 / 40/60 = 5.625 km/h     ..... (b(iii))


Study Tips for Answering NCERT Questions:

NCERT questions are designed to test your understanding of the concepts and theories discussed in the chapter. Here are some tips to help you answer NCERT questions effectively:

  • Read the question carefully and focus on the core concept being asked.
  • Reference examples and data from the chapter when answering questions about Motion in a straight Line.
  • Review previous year question papers to get an idea of how such questions may be framed in exams.
  • Practice answering questions within the time limit to improve your speed and accuracy.
  • Discuss your answers with your teachers or peers to get feedback and improve your understanding.

Notice: Undefined index: quesId in /var/www/html/ss_beta/saralstudy/ss_new/web/template/common/comment_section.php on line 3

Comments

Comment(s) on this Question

Welcome to the NCERT Solutions for Class 11 Physics - Chapter . This page offers a step-by-step solution to the specific question from Excercise 1 , Question 14: A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km h –1....