TBR physics circuits

[letmebeanMD]

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Example 9.4a
Which formula represents the time it takes to accelerate a car of mass m from rest to a speed v, using an electric motor with voltage V and drive current I?
A. t-2EI/mv2
B. t=2Iv/ mV
C. t=mv2/2IV
D. t=2lV/2Iv
Solution
We usually approach this kind of problem by thinking about units and limiting cases. If you are not too handy with electrical units (especially how they relate to mechanics units), then avoid checking units-you can't check what you don't know. Try limiting cases.
You need to think about how I, V, m, and v affect the acceleration time t. Think first about the one that is easiest for you to grasp conceptually. For example, if the car is to reach a higher speed v, what should happen to t? It should go up. Therefore, the answer is either B or C. Between these two choices, I and m are switched-V is not. Considering voltage would be a waste of effort-think

.If the current I increases,what should happen to t? It should decrease; after all, there is more current to make the car go. This leads to choice C.

PLEASE EXPLAIN BOLDED PARTS

 

[Temperature101]

Example 9.4a
Which formula represents the time it takes to accelerate a car of mass m from rest to a speed v, using an electric motor with voltage V and drive current I?
A. t-2EI/mv2
B. t=2Iv/ mV
C. t=mv2/2IV
D. t=2lV/2Iv
Solution
We usually approach this kind of problem by thinking about units and limiting cases. If you are not too handy with electrical units (especially how they relate to mechanics units), then avoid checking units-you can't check what you don't know. Try limiting cases.
You need to think about how I, V, m, and v affect the acceleration time t. Think first about the one that is easiest for you to grasp conceptually. For example, if the car is to reach a higher speed v, what should happen to t? It should go up. Therefore, the answer is either B or C. Between these two choices, I and m are switched-V is not. Considering voltage would be a waste of effort-think

.If the current I increases,what should happen to t? It should decrease; after all, there is more current to make the car go. This leads to choice C.

PLEASE EXPLAIN BOLDED PARTS

We know that power is: P = work/time . or P = Energy/ time... If we replace power by:

VI = E/t. ...E = VIt..... Let apply the work/energy theorem

E (electrical energy) = E (kinetic energy)

VIt = 1/2mv^2 ...t = mv^2/2VI

I think you should look at it in term of mass...As the mass increases, the car will have a lower speed; consequently, will take more time.