Q) The speed of a motor boat is 20 km/hr. For covering the distance of 15 km the boat took 1 hour more for upstream than downstream.

1. Let speed of the stream be x km/hr. Then speed of the motorboat in upstream will be
a) 20 km/hr           b) (20 + x) km/hr         c) (20 – x) km/hr            d) 2 km/hr

2. What is the relation between speed, distance and time?
a) speed = (distance )/time         b) distance = (speed )/time
c) time = speed x distance         d) speed = distance x time

3. Which is the correct quadratic equation for the speed of the current?
a) x² + 30x − 200 = 0                     b) x² + 20x − 400 = 0
c) x² + 30x − 400 = 0                     d) x² − 20x − 400 = 0

4. What is the speed of current?
a) 20 km/hour       b) 10 km/hour           c) 15 km/hour             d) 25 km/hour

5. How much time boat took in downstream?
a) 90 minute          b) 15 minute               c) 30 minute                 d) 45 minute

Ans:

Speed is always given by

Since, time taken to travel =

∴ Time taken upstream =

Similarly,  Time taken downstream =

∴

∴

∴

5.  As calculated in part 3, Time taken downstream =

=

= = 0.5 hrs = 30 mins

Check: Time taken upstream = = 1.5 hrs

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