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Grade: 12
        
A car is travelling on straight level road with a uniform speed of 60kmph it is followed by another car B which is moving with speed of 70kmph when the distance between them is 2.5km the car Back is given a deceleration of 20km/h2 after what distance of time B will catch up with A
11 months ago

Answers : (2)

Khimraj
3008 Points
							
Suppose the car B catches up with the car A in t hours. The distance travelled by the car Amoving with a velocity of 60 km h
-1
 in time hours is given by s
1
 = 60 t km.The distance traveled by the car B moving with an initial velocityu = 70 km h
-1
 and decelerated at the rate of 20 km h
-2
 in time t hours is given bys
2
 = ut + ½ at
2
 = 70t + ½ (-20)t
2
 = 70t - 10t
2
 But (s
2
-s
1
) = 2.5 km.·. 70 t -10 t
2
 - 60 t = 2.5 => 10t
2
 - 10t + 2.5 = 0.·. t
2
 - t + 0.25 = 0 => (t - 0.5)
2
 = 0=> t = ½ hSubstituting t = ½ h, we get s
2
 = 32.5 km.
11 months ago
Khimraj
3008 Points
							
s2 = ut + ½*a*t2 = 70t + ½*(-20)*t2 = 70t -10t2
s1 = 60t
s2 – s1 = 2.5
70t – 10t2 -60t = 2.5
10t2 -10t + 2.5 = 0
so t = ½ h
putting this in s2
s2 = 32.5km
Hope it clears.
 
11 months ago
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