Question

3. Two parallel rail tracks run north-south. Train A moves north with a speed of 27 km/hr, and train B moves south with a speed of 45 km/hr. What is the velocity of B with respect to A in m/s? Choose the positive direction of the x-axis to be from the south to north
: a)-18 b)-28 C) -20 d) -15​

Answer 1

Given: Train A moves north with speed 27 km/h and train B moves with speed 45 km/h.

To find: Velocity of B with respect to A in m/s

Explanation: To convert km/h to m/s, we divide the value with 3.6

27 km/h = 27 / 3.6= 7.5 m/s

45 km/h = 45/ 3.6 = 12.5 m/s

Since, the positive direction of x axis is taken to be from south to north, the speed of train going north is taken to be positive and speed to train going south is taken to be negative.

Therefore, speed of A = 7.5 m/s

Speed of B= - 12.5 m/s

Velocity of B with respect to A= Velocity of B- Velocity of A

= -12.5 - 7.5 m/s

= -20 m/s

Therefore, velocity of B with respect to A is -20 m/s.

Answer 2

Answer:

a.

v

BA

=

v

B

-

v

A

Hence, velocity of train B w.r.t train A is 144 km/h toward south.

b. Velocity of ground w.r.t. B

v

g,B

=v

g

−v

B

= 0 - 90$$

v

g,B

= -90 km/h

Hence, velocity of ground w.r.t train B is 90 km/h towards north.

c.

v

m,g

=

v

m,A

+

v

Ag

= 18 - 54 = -36 km/h

Hence, velocity of monkey will be 36 km/h toward north.