a) Let's call x the direction parallel to the river and y the direction perpendicular to the river.
Dave's velocity of 4.0 m/s corresponds to the velocity along y (across the river), while 6.0 m/s corresponds to the velocity of the boat along x. Therefore, the drection of Dave's boat is given by:

relative to the direction of the river.
b) The distance Dave has to travel it S=360 m, along the y direction. Since the velocity along y is constant (4.0 m/s), this is a uniform motion, so the time taken to cross the river is given by

c) The boat takes 90 s in total to cross the river. The displacement along the y-direction, during this time, is 360 m. The displacement along the x-direction is

so, Dave's landing point is 540 m downstream.
d) If there were no current, Dave would still take 90 seconds to cross the river, because its velocity on the y-axis (4.0 m/s) does not change, so the problem would be solved exactly as done at point b).
Answer:
last option
Explanation:
photovoltaic cell is when the sun's energy will be converted to as electricity causing an effect to create light for houses
Answer: 16.09m/s
Explanation:
Given the acceleration a(t) = 10/(t+1), to derive the velocity function, we need integrate the acceleration function.
v(t) = integral{10/t+1}dt
Since all constants always come out of the integral, the equation becomes;
v(t) = 10integral{1/t+1}dt
One of the integral law is that if the numerator of the function to be integrated is the differential of the denominator, the resulting answer will be natural logarithm of the denominator i.e ln(t+1) since the denominator is ln(t+1) and if differentiated will give us 1 which is the numerator hence, the reason for the answer ln(t+1)
v(t) = 10ln(t+1)
@ t= 4, the velocity of the particle
v(4) = 10ln(4+1)
v(4) = 10ln5
v(4) = 16.09m/s²
Therefore, the velocity of the particle at time t=4 is 16.09m/s