Question

Train A and train B are running on ·parallel tracks in opposite directions with speeds 36 km/hour and 72 km/hour, respectively A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km/hour. Speed (in ms^-1) of this person as observed from train B will be close to: (take the distance between the tracks as negligible)

विकल्प

• 30.5 m s^-1

• 29.5 m s^-1

• 31.5 m s^-1

• 28.5 m s^-1

Answer 1

29.5 m s^-1

Explanation:

Given: Speed of train A, v_A = 36 km/hr, speed of train B, v_B = 72 km/hr, both the trains are moving in opposite direction, speed of a person walking inside train A, v_p = 1.8 km/hr, v_P is parallel to v_B.

To find: The speed of the person as observed from train B in m/s, v'_p.

Let train A be moving in -x-direction and train B be moving in +x-direction. So, velocity of train A as observed from train B is:

v'_A = (-72 - 36) km/hr = 108 km/hr = 30 m/s

Velocity of person (the person is moving in +x direction):

v_P = +1.8 km/hr = 0.5 m/s

Now, velocity of the person as observed by train B:

v'_p = [-30-(0.5)] m/s = -29.5 m/s

Hence, the magnitude of velocity is

|v'_p| = 29.5 m/s