Susan is standing in an empty Metro (subway) car which is travelling at constant

Question

Susan is standing in an empty Metro (subway) car which is travelling at constant velocity. Suddenly, because of an emergency, the driver applies the brakes. Select True or False for each of the following statements.

1. If she immediately grabs onto the seat behind her (she is facing forwards), then she must pull on the seat to avoid falling.

2. She falls because there is no force acting on her which can be large enough to slow her down.

3. She falls forwards -- i.e. towards the front of the car.


4. If she immediately jumps straight up into the air, she will land closer to the back of the car.

Thank you!

Explanation / Answer

1. True - This one is worded strange but if you think about it just holding on is like pulling on the seat which would stop her from moving forward. 2. True - She is free standing so no force is acting on her when the train stops. 3. True - Think about it like your in a car and you suddenly apply the breaks, you fall forward until your seat belt stops you and if your not wearing one you hit the dash. This is the same concept but with the floor. 4. False - If she jumped she would be going the same speed as the car was originally but the car would be traveling slower under her causing her to move towards the front of the car. This can be proved with kinematics.

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