Question : From the figure find the ratio of speed in first two seconds to the speed in the next four seconds.
Doubt by Japjee
Solution :
We know, the slope of distance (s) - time (t) graph gives speed (v).
Speed of the body during the first two seconds
v1=Slope of OA
v1=(s-0)/(2-0)
v1=s/2 — (1)
v1=(s-0)/(2-0)
v1=s/2 — (1)
Speed of the body during the next four seconds
v2=Slope of AB
[B is the point where the coordinate is (6,0)]
v2=(0-s)/(6-2)
v2=(0-s)/(6-2)
v2=-s/4
But v2 is speed, which can't be -ve. so we neglect the -ve sign.
v2=s/4 — (2)
Required ratio will be given by dividing equation (1) by (2)
v1/v2 = [s/2]/[s/4]
v1/v2=4/2
v1/v2 = 2/1
v1:v2 = 2:1
v1/v2=4/2
v1/v2 = 2/1
v1:v2 = 2:1