A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3.0 km upstream. If the river flows at 5m/s ,the time required for this round trip is:
a) 120s
b) 150s
c) 200s
d) 300s
e) 320s

Time required for round trip is 320 s.

Explanation:

Given :

Velocity of boat in still water , v = 20 m/s.

Velocity of river , V = 5 m/s.

In the given question boat make round trip to a town 3 km upstream.

Therefore, Total time = time taken in upstream + time taken in upstream.

We know ,   ( here all have their usual meaning ).

Total time ,    ( upstream velocity = 20-5 = 15 m/s.

                                                              downstream velocity = 20+5 = 25 m/s)

Hence, this is the required solution.

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

the answer is a)

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