EK #46 Physics

[Addallat]

Can somebody explain how to arrive to an answer for the following question:

A particle travels 3.5 m. If its initial velocity is 9 m/s and its final velocity is 16 m/s. What is its acceleration?


A. 1 m/s^2
B. 2 m/s^2
C. 7 m/s^2
D. 25 m/s^2



My solution was:

V^2 = Vo^2 + 2 (a) (d) ~~~~~> (V^2-Vo^2) / (2d) = a

(16^2 - 9^2) / 7 = a

The answer comes out to D but damn I have such a hard time finding a way to simplify the math.... this seems to be the case for the majority of physics problems I come across can somebody please give me some suggestions? Are others out there really able to do the math quickly in their head? I'm staring to feel like the physical sciences are going to kill me solely on the fact that my ability to do simple math quickly sucks!

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[AureatEagle]

Can somebody explain how to arrive to an answer for the following question:

A particle travels 3.5 m. If its initial velocity is 9 m/s and its final velocity is 16 m/s. What is its acceleration?


A. 1 m/s^2
B. 2 m/s^2
C. 7 m/s^2
D. 25 m/s^2



My solution was:

V^2 = Vo^2 + 2 (a) (d) ~~~~~> (V^2-Vo^2) / (2d) = a

(16^2 - 9^2) / 7 = a

The answer comes out to D but damn I have such a hard time finding a way to simplify the math.... this seems to be the case for the majority of physics problems I come across can somebody please give me some suggestions? Are others out there really able to do the math quickly in their head? I'm staring to feel like the physical sciences are going to kill me solely on the fact that my ability to do simple math quickly sucks!

This is a fair calculation question which you really should be able to work out in a reasonable amount of time. It gets faster with practice.

However, I also took the time to memorize all the squares from 11-25. It was a massive help, as you're dealing with squaring calculations very frequently. Worth the time investment, I think.

Also, keeping calm when doing calculations on the real thing is a must. It's easy to get freaked out while working out the calculations for a problem because it feels like it's taking a while, and you tend to make more silly mistakes in this state. Get used to it-- the PS may or may not be calculation heavy for your test!

 

[Addallat]

been staring at this problem between my other practice problems

1st: noticed I could solve for time

(d)2/(vo+vf) = t

7/25 ~~~> 1/5

2nd: a = vf-vo/ (1/5)

5*5 = 25 BAM answer is D

i hate you physics.

 

[catzzz88]

been staring at this problem between my other practice problems

1st: noticed I could solve for time

(d)2/(vo+vf) = t

7/25 ~~~> 1/5

2nd: a = vf-vo/ (1/5)

5*5 = 25 BAM answer is B

i hate you physics.

You might want to check your math one more time!

Best,
C

 

[Addallat]

meant to say choice D*

1st equation rounded 7/25 to 5/25 to make life easier

also wound up rounding deltaV = 7 down to 5 for the 2nd equation to get 25 as the answer; although if i would have left it as 7 the answer would have been 35 and using POE from the answer choices D was obvious


without any rounding 7/.28= 25 so saved major time with the rounding

 

[Rhino1000]

Can somebody explain how to arrive to an answer for the following question:

A particle travels 3.5 m. If its initial velocity is 9 m/s and its final velocity is 16 m/s. What is its acceleration?


A. 1 m/s^2
B. 2 m/s^2
C. 7 m/s^2
D. 25 m/s^2



My solution was:

V^2 = Vo^2 + 2 (a) (d) ~~~~~> (V^2-Vo^2) / (2d) = a

(16^2 - 9^2) / 7 = a

The answer comes out to D but damn I have such a hard time finding a way to simplify the math.... this seems to be the case for the majority of physics problems I come across can somebody please give me some suggestions? Are others out there really able to do the math quickly in their head? I'm staring to feel like the physical sciences are going to kill me solely on the fact that my ability to do simple math quickly sucks!

This is a "doable in your head" problem. Think about it. In the 3.5 meters, the average speed the particle travels is about 12.5 m/s. This means that it took about a quarter of a second to travel that 3.5 meters, and therefore a quarter of a second to accelerate from 9 to 16 meters per second. This means that the acceleration is about 7 m/s, per ~quarter of a second.

7 (m/s) / (about a quarter of a second) is about 28 +-5 M/S^2.

(That's how I did the problem.)