A crew team rows a boat at a rate of 20 km/h in still water. Beginning at time = 0 minutes, the team rows for 30 minutes up a ri
ver (against the current). The speed of the current is 1.5 km/h. How long will it take the crew team to row down the river (with the current) to return to the starting point? 22 min
26 min
24 min
30 min
Since they are rowing against the current, their velocity realtive to the groud is 20-1.5 = 18.5km/h So the distance travelled is 18.5km/h*0.5h = 9.25km Going back with the current their ground realative velocity is 20+1.5 = 21.5km/h so the time it takes them to return 9.25 km is 9.25km/(21.5km/h) = 0.43h ~= 26 min
The emf is equal to the work done on the charge per unit charge (ϵ=dWdq) when there is no current flowing. Since the unit for work is the joule and the unit for charge is the coulomb, the unit for emf is the volt (1V=1J/C).
The direction of the acceleration is in the same direction as the net force causing it. F = ma is actually a vector equation in which f and a are both vectors and m is a scalar constant.
