The answer is above but I don't know if it's correct.
Answer:
Option e) 320 s
Explanation:
Here, distance = 3.0 km = 3000 m
The velocity of boat when it is going upstream;
Upstream velocity = velocity of boat in still water - velocity of river flow
So, Upstream velocity 
So,Time to go upstream

The velocity of boat when it is going downstream;
Downstream velocity = velocity of boat in still water + velocity of river flow
So, Downstream velocity 
So,Time to go downstream

So, total time (t) = 
Option E is the correct answer.
Answer:19.32 m/s
Explanation:
Given
initial speed of car(u)=4.92 m/s
acceleration(a)=
Speed of car after 4.5 s
using equation of motion
v=u+at

v=19.32 m/s
Displacement of the car after 4.5 s



s=54.54 m
Answer:
<h2>E. 3.95kW</h2>
Explanation:
Power is defined as the rate of workdone.
Power = Workdone/time taken
Given Workdone = Force * distance
Power = Force * distance/time taken
Power = mgd/t (F = mg)
m = mass of the sand in kg
g = acceleration due to gravity in m/s²
d = vertical distance covered in metres
t = time taken in seconds
Given m = 2000kg, d = 12m, t = 1min = 60secs, g = 9.8m/s²
Power = 2000*9.8*12/60
Power = 3920Watts
Minimum rate of power that must be supplied to this machine is 3920Watts or 3.92kW