In 8 seconds and 20 seconds, a train passes by a telegraph post and a 264-meter-long bridge, respectively. What is the train's top speed?
A. 69.5 km/hr
B. 70 km/hr
C. 79 km/hr
D. 79.2 km/hr
Answer:D
In 8 seconds and 20 seconds, a train passes by a telegraph post and a 264-meter-long bridge, respectively. What is the train's top speed?
A. 69.5 km/hr B. 70 km/hr C. 79 km/hr D. 79.2 km/hr
Explanation: Assume the train's length is x metres and its speed is y metres per second.Then, x/y = 8 => x = 8y; now, x + 264/20 = y => 8y + 264 = 20y => y = 22; now, x + 264/20 = y => 8y + 264 = 20y => y = 22.As a result, Speed = 22 m/sec equals ( 22 x 18/5 ) km/hr = 79.2 km/hr.