Answer:C
Explanation:
When a constant horizontal force is applied to the box, box started moving in the horizontal direction such that it moves with constant velocity 
Constant velocity implies that net force on the box is zero
i.e. there must be an opposing force which is equal to the applied force and friction force can serve that purpose.
So option c is the correct choice.
Answer:
The middle and end of the string respectively
Explanation:
Rarefaction means region of maximum displacement and compression means region of minimum displacement, hence.
We expect a maximum displacement at the middle of the string because it is said to vibrate greatest at this point and conversely vibrate least at the end point which is the region of compression.
Time = 7200 s. 3600 s = 1hour.
7200s = 7200 / 3600 = 2 hours.
Speed = Distance / time = 150 km / 2 hours = 75 km/h
I might be incorrect but I’m pretty confident that all of it is right. I think you’re good.
