# Tutor profile: Bobby A.

## Questions

### Subject: Physics (Newtonian Mechanics)

How should I solve a problem that involves a bullet of known mass and velocity being fired into a stationary block and sticking in it, if it asks me to find the velocity of the block?

Problems like these want you to express a knowledge of conservation of momentum. This means that in a closed system, such as the one set up in the question, the total momentum before the event and the total momentum after the event must be the same. So by finding the momentum of the bullet before collision (found by multiplying mass times velocity in standard units), and setting it equal to the momentum of the block with the bullet inside after the collision (which would have a mass of the block plus the bullet), you can find the final velocity of the block bullet pair.

### Subject: Basic Chemistry

How do I know if a bond is ionic or covalent?

Ionic bonds occur between a metal and a non-metal, and covalent bonds occur between two non-metals. For example, Potassium is a metal, and Fluorine is a non-metal (this is known because of their locations on the periodic table) if these two bond to form Potassium Fluoride (KF), then it is an ionic bond. However, since Carbon and Hydrogen are both non-metals, if they bond to form Methane (CH4), then that is a covalent bond.

### Subject: Calculus

How do I know if a line has a positive or negative derivative?

The derivative is the rate of change of the line. In most graphs it is the rate of change of Y as it relates to X, meaning if Y is getting bigger as X gets bigger (also known as having a positive slope), then the derivative will be positive. However, if Y is getting smaller as X is getting bigger (also known as having a negative slope), then the derivative will be negative.

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