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

The Correct Option is A

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