Laws of motion Online 2018 mains
Q.21. A man in a car at location Q on a straight highway is moving with speed v. He decides to reach a point P in a field at a distance d from the highway (point M) as shown in the figure. Speed of the car in the field is half to that on the highway. What should be the distance RM, so that the time taken to reach P is minimum ?


1. d 3
2. d 2
3. d
4. d 2

Dear Student,
let the distance between the Q and M is Llet RM is xtime taken to reach Pt=L-xv+2d2+x2vdifferentiate above wrt xdtdx=-1v+2v2x2d2+x2=0xd2+x2=122x=d2+x2d2+x2=4x2d2=3x2x=d3 for this value the time be minimum.option 1Regards

  • 1
What are you looking for?