Awoman can row a boat at 7.80 km/h in still water. (a) if she is crossing a river where the current is 3.90 km/h, in what direction must her boat be headed if she wants to reach a point directly opposite her starting point? express your answer as an angle with respect to the line perpendicular to the river, positive if down the river. (b) if the river is 7.80 km wide, how long will she take to cross the river? (c) suppose that instead of crossing the river she rows 3.90 km down the river and then back to her starting point. how long will she take? (d) how long will she take to row 3.90 km up the river and then back to her starting point? (e) in what direction should she head the boat if she wants to cross in the shortest possible time, and (f) what is that time?

Athin plate moves between two parallel, horizontal, stationary flat surfaces at a constant velocity of v = 7.5 m/s. the two stationary surfaces are spaced 4 cm apart, and the medium between them is filled with oil whose viscosity is 0.9 n·s/m2. the part of the plate immersed in oil at any given time is 2 m long and 0.5 m wide. if the plate moves through the mid-plane between the surfaces, determine the force required to maintain this motion. what would your response be if the plate was 1 cm from the bottom surface (h2) and 3 cm from the top surface (h1)? if the plate moves through the mid-plane between the surfaces, the force required to maintain the motion will be n. if the plate was 1 cm from the bottom surface (h2) and 3 cm from the top (h1) surface, the force required to maintain the motion would be n.

Immediately upon reaching its lowest point, a falling pendulum bob has its greatest amount of energy, which is the initial amount of potential energy. a. heat; less than b. heat; more than c. kinetic; less than d. kinetic; more than

(2) (a) you have a simple circuit that consists of only a battery (δvbat=1.5v) and two resistors with resistance r1=10ω and r2=5ω, connected in series with each other. what is the current running through the battery? (b) you re-arrange your circuit so now r2 is attached in parallel to r1 rather than in series. what is the current running through the battery? (c) you add an additional resistor r3=7ω on the same branch as r2. what is the current running through the battery? (d) what is the power dissipated in r3?