Places A and B are 80 km apart from each other.A car starts from A and other from B at the same time.If they move in the same direction,they meet in 8 hours and if they move in opposite direction they meet in 1 hour and 20 minutes.find speed ?

1 Answer
Aug 2, 2018

Answer:

The speeds are #v_A=70/2=35kmh^-1# and #v_B=25kmh^-1#

Explanation:

Let the speeds of the cars be

#=v_Akmh^-1#

and

#=v_Bkmh^-1#

Firstly, for the cars moving in the same direction

Let the distance travelled by the second car be #=dkm#

Then,

#80+d=8v_A#

#d=8v_B#

Combining these #2# equations

#80+8v_B=8v_A#

#8(v_A-v_B)=80#

#(v_A-v_B)=10#................................#(1)#

Secondly, for the cars moving in the opposite direction

Let the distance travelled by the second car be #=xkm#

Then,

#80-x=4/3v_A#

#x=4/3v_B#

Combining these #2# equations

#80-4/3v_B=4/3v_A#

#4/3(v_A+v_B)=80#

#v_A+v_B=60#.........................................#(2)#

Solving equations #(1)# and #(2)#

#v_A=70/2=35kmh^-1#

#v_B=25kmh^-1#