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02 Sep 2021, 03:38
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
92% (01:26) correct
8%
(02:23)
wrong
based on 118
sessions
History
Date
Time
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Not Attempted Yet
The speed of a train pulling out of a station is given by the equation \(s = t^2 + t\), where s is the speed in kilometers per hour and t is the time in seconds from when the train starts moving. The equation holds for all situations where \(0 ≤ t ≤ 4\). In kilometers per hour, what is the positive difference in the speed of the train 4 seconds after it starts moving compared to the speed 2 seconds after it starts moving?
(A) 0
(B) 6
(C) 14
(D) 20
(E) 38
(A) 0
(B) 6
(C) 14
(D) 20
(E) 38
02 Sep 2021, 03:54
Kudos
Bookmarks
Bunuel
Solution:
We are given an expression to find out the speed of a train as \(s = t^2 + t\), where s is the speed in kilometers per hour and t is the time in seconds.
So the speed of the train \(2\) seconds after it starts moving \(⇒ s_2=2^2+2=4+2=6 kmph\).
And speed of the train \(4\) seconds after it starts moving \(⇒ s_4=4^2+4=16+4=20 kmph\).
The difference \(s_4-s_2=20-6=14. \)
Hence the right answer is Option C.
05 Sep 2021, 01:14
Kudos
Bookmarks
What about the units? Shouldn't the seconds be converted to hours or vice versa?
