# Rocket Thrust Question (1 Viewer)

#### 123ryoma12

##### Member
Question:

Why is it wrong to do initial thrust = final thrust when the question says that the thrust remains constant?
My attempt:
http://i.imgur.com/9rVtCIO.jpg
Maybe I'm subbing values wrong?

##### Member
use the equation a=(T-mg)/m and it should turn out right

#### 123ryoma12

##### Member
New Question plz Help Again

#### 123ryoma12

##### Member
Where's the question part of this question?
it was
"How much electrical energy was converted to other forms of energy by the light globe?"

mgh - KE

#### 123ryoma12

##### Member
plz help again

How do I find out if the answer is either B or D. I'm not sure how to apply lenz law in this.

#### 1008

##### Active Member
plz help again
View attachment 33560
View attachment 33561
How do I find out if the answer is either B or D. I'm not sure how to apply lenz law in this.
For this one, you don't apply Lenz's Law - at least not in my approach.

In fact, you apply the Left Hand Curl Rule (LHCR). As the CRO shows a wavy voltage (not a straight line), you can deduce that this is AC and not DC. So you can eliminate A and C because they have a split ring commutator which is characteristic of DC.

Now look at the X and Y positions in the options and your AC voltage graph. Initially, the current is positive, so that means that current is flowing into X (i.e. current is flowing in the direction of the arrow at X in the options). This means current is travelling out of the page in the coil, so you point your left thumb towards you. You'll notice that the curve of your hand is clockwise - and this is the direction the handle must be rotated in.

#### 123ryoma12

##### Member
For this one, you don't apply Lenz's Law - at least not in my approach.

In fact, you apply the Left Hand Curl Rule (LHCR). As the CRO shows a wavy voltage (not a straight line), you can deduce that this is AC and not DC. So you can eliminate A and C because they have a split ring commutator which is characteristic of DC.

Now look at the X and Y positions in the options and your AC voltage graph. Initially, the current is positive, so that means that current is flowing into X (i.e. current is flowing in the direction of the arrow at X in the options). This means current is travelling out of the page in the coil, so you point your left thumb towards you. You'll notice that the curve of your hand is clockwise - and this is the direction the handle must be rotated in.
Initially the voltage of X is positive doesn't that mean that current is initially flowing at Y and electrons are flowing to X?