GIVEN: Distance between two cars = 64 km apart Speed of one car = 48 km/h t1−t2=30 CONCEPT: Speed, time and distance FORMULA USED: Distance = Speed × Time CALCULATION: Let speed of second car = ‘x’ Relative speed of cars = (48 + x) Now, 64 − 4 = (48 + x) ×
t1
60
⇒ (48 + x) t1 = 3600 ...1) 84 − 64 = (48 + x) ×
t2
60
⇒ (48 + x) t2= 1200 ...2) From (1) and (2): t1 / t2 = 3/ 1 Let t1 = 3a and t2= a t1−t2=30 ⇒ 3a – a = 30 ⇒ a = 15 (48 + x) × 3 × 15 = 3600 ⇒ 48 + x = 80 ⇒ x = 32 ∴ Speed of second car = x = 32 km/h