Chapter-2 Q032 - Physics For Engineers And Scientists - Solutions

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Question 32 - Problems - Chapter 2

Problem:

A dog runs 35 m to catch a Frisbee in 4.5 s, turns quickly and trots 22 m back in 3.6 s, but then stops to guard the Frisbee.

Question:

a) What is the dog's average speed?

b) What is the dog's average velocity?

Solution:

The dog does not return completely so $\Delta s = 35m - 22m = 13m$

The way the dog traveled is $s = 35 + 22 = 57$ m

The time to complete his track is $t = 4.5 + 3.6 = 8.1s$

In [1]:
import numpy as np
d_s = 13
s = 57
t = 8.1
v_v = d_s / t
v_s = s/t
print(f'a) The dog\'s average speed is: {v_s:.1f} m/s')
print(f'b) The dog\'average velocity is: {v_v:.1f} m/s')
a) The dog's average speed is: 7.0 m/s
b) The dog'average velocity is: 1.6 m/s

سُوۡرَةُ حٰمٓ السجدة / فُصّلَت
ثُمَّ اسْتَوَىٰ إِلَى السَّمَاءِ وَهِيَ دُخَانٌ فَقَالَ لَهَا وَلِلْأَرْضِ ائْتِيَا طَوْعًا أَوْ كَرْهًا قَالَتَا أَتَيْنَا طَائِعِينَ ﴿١١
فَقَضَاهُنَّ سَبْعَ سَمَاوَاتٍ فِي يَوْمَيْنِ وَأَوْحَىٰ فِي كُلِّ سَمَاءٍ أَمْرَهَا ۚ وَزَيَّنَّا السَّمَاءَ الدُّنْيَا بِمَصَابِيحَ وَحِفْظًا ۚ ذَٰلِكَ تَقْدِيرُ الْعَزِيزِ الْعَلِيمِ ﴿١٢


Surah Fussilat: Thereafter turned He to the heaven and it was as smoke, and said Unto it and Unto the earth: come ye twain, willingly or loth. They said: we come willingly. (11) Then He decreed them as seven heavens in two days, and revealed Unto each heaven the command thereof; and We bedecked the nether heaven with lamps and placed therein a guard. That is the ordinance of the Mighty, the Knower. (12)

De hemelen en aarde (waren) een samenhangende massa. Wij hebben ze toen van elkaar gescheiden… Wij hebben de hemel tot een beschermend dak gemaakt … en de dag en de nacht, de zon en de maan geschapen. (Koran 41 11:12)


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