Answer to Question #119566 in Physics for Joseph Wisdom

Question #119566
A man traveled a distance of 120km by car from hisme to Lagos. On his way back, his average speed was increased by 5km/h and he found out that he took 20mins less
a. What was his average speed for the first part of the journey?
b. How long did he take for the double journey
1
Expert's answer
2020-06-02T17:53:00-0400

Let the speed of a car for the first part of the journey is v1v_1. Then time of motion for the first part of the journey

t1=120v1t_1=\frac{120}{v_1}

For the second part we get


t11hr3=120v1+5t_1-\frac{1{\rm hr}}{3}=\frac{120}{v_1+5}

Hence

120v113=120v1+5\frac{120}{v_1}-\frac{1}{3}=\frac{120}{v_1+5}

120v1120v1+5=13\frac{120}{v_1}-\frac{120}{v_1+5}=\frac{1}{3}

Root

v1=40km/hrv_1=40\:\rm km/hr

Thus


t1=12040=3hrt_1=\frac{120}{40}=3\:\rm hr

t2=t11/3=31/3=2hr40mint_2=t_1-1/3=3-1/3=2\rm\: hr\:40\: min

Total time of motion


t=t1+t2=5hr40mint=t_1+t_2=5\rm\: hr\:40\: min

Answers:

(a) 40km/hr40\:\rm km/hr

(b) 5hr40min5\rm\: hr\:40\: min


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Comments

Unknown Person
21.11.21, 21:01

Thanks :)

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