2 more physics problems...

[fluffinski08]

Cearly I'm having a hard time with physics! Here are two problems I didn't understand:

1) If two vectors with magnitudes of 100 and 50 are added, which one of the following is the only possible answer for the magnitude of the resultant? (the answer is 75).

2) A truck starts from rest. When it has covered a distance of 45m in one direction, its speed is 30 m/s. How long did it take the truck to attain this velocity? (answer is 3 seconds).

Thank you so much in advance!!

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[FutureInternist]

Cearly I'm having a hard time with physics! Here are two problems I didn't understand:

1) If two vectors with magnitudes of 100 and 50 are added, which one of the following is the only possible answer for the magnitude of the resultant? (the answer is 75).

2) A truck starts from rest. When it has covered a distance of 45m in one direction, its speed is 30 m/s. How long did it take the truck to attain this velocity? (answer is 3 seconds).

Thank you so much in advance!!

1) sin 30 or cos 60 = 1/2, so I would assume that the other answer choices were such that sin or cos of none of the normal angles used in MCAT could give the resultant vector (45, 90 etc)
So if the 100 vector was horizontal (going L--> R) & the 50 vector was making a 60" angle w/ it (going R --> L) you would get 75; since cos60*50 = 25 which you would subtract from 100

2) Using v^2 - u^2 = 2as (with v=30, u=0, s=45), you get the acceleration as 10m/s^2.....therefore it would take 3 secs to get to 30m/s

It's been a while since I did a physics problem so please double check

 

[fluffinski08]

Thanks! That really helped!