Question

The speed of a train pulling out of a station is given by the equation s = t2 + 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 were o __t __4. In kilometers per hour, what is the difference in the speed of the train four seconds after it starts moving, compared to the speed two seconds after it starts moving?

• A. 14
• B. 6
• C. 0
• D. 20

Answer 1

Answer: (A)

14

Answer 2

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 22 seconds after it starts moving ⇒ s_2=2^2+2=4+2$$=6kmph
And speed of the train 44 seconds after it starts moving ⇒ $s_4=4^2+4=16+4=20kmph$
The difference $s_4-s_2=20-6=14$
The correct option is (A): 14