A moving sidewalk has a velocity of 1.3 m/s north. If a man walks south on the sidewalk at a speed of 0.9 m/s, how long does it take him to travel 20 m relative to a stationary observer? O A. 21.9 s B. 15.4 s O C. 33.3 O D. 50.0 S help please!!!

D: 50 s

Explanation:

We are told that the sidewalk has a velocity of 1.3 m/s north.

Also, we are told that the man walks south on the sidewalk at a speed of 0.9 m/s.

Thus, it means they are moving in opposite directions. The net velocity of the man will be;

v_net = 1.3 - 0.9

v_net = 0.4 m/s

We want to find how long does it take him to travel 20 m relative to a stationary observer,thus;

We we know that;

Time = distance/speed

Time = 20/0.4

Time = 50 s

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )