If the box is moving at constant velocity, net force must be zero, so:
F + fr = 0
fr = -F
<u>fr = -40 N</u>
Answer:
The time is
Explanation:
From the question we are told that
The period of the circuit is 
Generally voltage maximization of the capacitor occurs during the voltage minimization of the inductor and vise versa
So the time between the voltage maximization of the capacitor and that of the inductor is mathematically represented as

=> 
=>
Average speed is the ratio of total distance moved by Chi in total time interval
So here we will have
Total distance = 100 m + 400 m

Total time taken = 5 min + 15 min = 20 min

now by the formula of average speed we know that



so average speed will be 1.5 km/h