electrical force strength

[ronaldo23]

this is from cbt 9 question 2:

If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will:

a. decrease by 2
b. remain same
c. increase by 2
d. increase by 4.

The answer is b, based on teh equation f=eq, and hence the only factors affecting the speed are the electric field and charge.

But I thought it was c., based on the equation eq=ma (which they use later in equation 4). I figure if the speed is increased by 2, the acceleration will also increase by 2, and ma doubles, and hence, eq must also double to keep up wtih that. Since F=eq, doesn't it logically follow that F increases by 2?

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[PiBond]

this is from cbt 9 question 2:

If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will:

a. decrease by 2
b. remain same
c. increase by 2
d. increase by 4.

The answer is b, based on teh equation f=eq, and hence the only factors affecting the speed are the electric field and charge.

But I thought it was c., based on the equation eq=ma (which they use later in equation 4). I figure if the speed is increased by 2, the acceleration will also increase by 2, and ma doubles, and hence, eq must also double to keep up wtih that. Since F=eq, doesn't it logically follow that F increases by 2?

the speed does not affect acceleration. and since the E field (and charge of the particle) is the same there's no additional force causing the particle to speed up. but regardless, the force on the particle is independent of speed and acceleration is only affected by the charge of the particle (increased charge increases force on charge) and E field (increase field increase force).

 

[ronaldo23]

why doesn't speed affect acceleration? isn't accerlation equal to the change in velocity/speed?

 

[Geekchick921]

Do they give you any additional information, like the amount of time it takes for the velocity to increase? If not, you definitely can't make any assumptions about the rate of acceleration.

 

[lixxx669]

why doesn't speed affect acceleration? isn't accerlation equal to the change in velocity/speed?

In my opinion, speed doesn't affect acceleration, but acceleration affect speed (acceleration cause speed to change).

But anyways, according to the question, it sounds like that if speed increases twice, but every thing else doesn't change, then what the F would be. Since the q, E and m stay the same, thus F stays the same too.

 

[Isoprop]

I don't have the question/passage in front of me but...

even if the particle was accelerating, there would be no change in electrical force. electrical force is dependent on the strength of E and q. In other words, the force is a function of E and q.

Once we figure out the force, we can describe its acceleration using F=ma. But acceleration doesn't "cause" a force, it simply describes if a force exists.

Think of it this way. Let's say I drop a ball onto the ground. The force of gravity is always mg throughout the time it takes to fall. It doesn't matter if the object has a velocity of zero when I just drop it or a velocity of 20 m/s right before it hits the ground, the force of gravity is always the same. Even if I accelerate the ball up with my hand, the force of gravity is still the same. It only depends on the mass of the ball and the value of "g."

Make sense?

 

[Econ2MD]

Big picture...the question is asking how the particle's velocity affects the electrical force applied to the particle.

F=qE

The only things that affect the electrical force applied to the particle are the particle's charge and the magnitude of the electric field it is traveling through.