- #1
SnowOwl18
- 71
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I'm back once more because of another problem that is driving me nuts. I've been trying to do this one for a long time. I'm posting the previous problem because it has relevant information and then bold typing the problem I'm confused on.
----Find the speed at which Superman (mass = 79 kg) must fly into a train (mass = 16351 kg) traveling at 80 km/hr to stop it. Calculate the time it takes Superman to stop the train, if the passengers experience an average horizontal force of 0.55 times their own weight. ------
And the hint they give for the problem is: Hint: The average horizontal force tells you the maximum acceleration of a passenger. With the change in speed in a given time, you can find the acceleration. Careful with units. Be sure to differentiate between weight and mass.
Ok...so I need to find the time it takes for Superman to stop the train. What I did was find the weight of the train...16351 kg x 9.8 m/s^2...and then multiplied that answer by 0.55 to the get the horizontal force, which I calculated to be 88131.89 N. I know that F=ma...so 88131.89 N = 16531 x A.
Acceleration is the change in velocity over the change in time. So I solved for A and got 5.33 m/s^2...the change in velocity is 1.66E+04 km/hr (which I found in the previous problem) - 80 km/hr = 16520 km/hr...
So 5.33 = 16520/T (change in time)...and I get 3099.44 s or hr...that I'm not sure of. Either way, the answer is wrong and I really don't know what I'm doing wrong.
If anyone can make any sense of what I wrote and see what I did wrong, I'd be grateful to know. Thanks so much. :)
----Find the speed at which Superman (mass = 79 kg) must fly into a train (mass = 16351 kg) traveling at 80 km/hr to stop it. Calculate the time it takes Superman to stop the train, if the passengers experience an average horizontal force of 0.55 times their own weight. ------
And the hint they give for the problem is: Hint: The average horizontal force tells you the maximum acceleration of a passenger. With the change in speed in a given time, you can find the acceleration. Careful with units. Be sure to differentiate between weight and mass.
Ok...so I need to find the time it takes for Superman to stop the train. What I did was find the weight of the train...16351 kg x 9.8 m/s^2...and then multiplied that answer by 0.55 to the get the horizontal force, which I calculated to be 88131.89 N. I know that F=ma...so 88131.89 N = 16531 x A.
Acceleration is the change in velocity over the change in time. So I solved for A and got 5.33 m/s^2...the change in velocity is 1.66E+04 km/hr (which I found in the previous problem) - 80 km/hr = 16520 km/hr...
So 5.33 = 16520/T (change in time)...and I get 3099.44 s or hr...that I'm not sure of. Either way, the answer is wrong and I really don't know what I'm doing wrong.
If anyone can make any sense of what I wrote and see what I did wrong, I'd be grateful to know. Thanks so much. :)