2012 Physics Fall Semester Exam Study

Guide: Additional Practice

Is it ok to bring bookbags, etc. into the lab area?

NO! This will clutter the lab area.

Why did Newton think the moon was accelerating?

He knew the moon was moving in a circle, and objects moving in a circle must have unbalanced forces accelerating them. (Otherwise they'd move in a straight line).

What are two key clues you are studying projectile motion?

1. The object's path of motion is curved.

2. Velocity over time can be determined.

If you break anything made of glass

in the lab, what's the BEST thing to do?

IMMEDIATELY NOTIFY THE TEACHER!!!

WARN OTHERS OF THE DANGER.

DON'T CLEAN UP YOURSELF!

What is meant by "terminal velocity"?

This is where speed (velocity) is constant b/c the force of gravity=the force of air resistance (so there are no unbalanced forces!)

Of all of today's sources of energy, which do you think would most likely result in frequent fluctuations?

Wind. Why? Because wind currents are variable throughout the day!

What is the NET FORCE acting on an object where there is a downward (south) force of 5 N and an

upward (North) force of 10 N?

If forces are opposite: SUBTRACT

If forces are same direction: ADD

So... 10N - 5N= 5N Northward Net force

Mechanical Energy=KE or PE

PE=mgh (mass * gravity * height)

KE=1/2mv2 (m=mass v=velocity)So...If an object has a velocity of 5 m/s and a mechanical

energy of 20J, what's its mass?

***Pick the right equation, based on what you know! KE=1/2 mv2 Solve for "m".

20J=.5m(5m/s2)

20J=.5m(25)

0.8J=.5m

m=1.6kg

If an object is moving at constant speed in a circle, what is the direction of force?TANGENT to the circle!

Why can't a ball bounce higher than the point it was released?

The law of conservation of energy says so!

PE gets converted to KE, but no extra energy can be created, so ball can't go higher than the height contributing to the original PE!

What is the ACCELERATION of any object when it is moving UPWARD/DOWNWARD?

If an object is moving upward, it is only battling the force of gravity, so the acceleration is the opposite of gravity, or -9.8m/s2.

Likewise, if an object is moving downward, it's only accelerated by gravity, so the acceleration is 9.8m/s2.

How many forces can be shown on an FBD (free body diagram)?

Forces can act in MANY different directions (NOT JUST 4!)

So...forces shown on a FBD should represent as many forces as are present!

Force of gravity between two objects

Force of gravity is DIRECTLY PROPORTIONAL to mass of objects & inversely proportional to distance between.

Equation: F=G x (m1m2/d2)

So if mass of one object triples and mass of the other doubles, simply multiply 3X2=6 to figure out how much the force of gravity increases.

Acceleration is DIRECTLY PROPORTIONAL to change in unbalanced forces!

So...If forces double, acceleration doubles!

Ex: 5N of force increases to 10N, so acceleration doubles to 2x's initial acceleration.

If forces are cut in 1/2, acceleration is too!

Ex: 10N of force decreases to 5N, so acceleration is 1/2 of what you started with...

Normal Force is AKA Support Force

So, in a FBD, the normal force is the one in the UPWARD direction (and so is the support force b/c they are the same thing!)

Ex:

MOMENTUM=Mass x Velocity (m x v)

So...If an object has a mass of 10kg and moves at a rate of 5 m/s for 20 s, what is the momentum?

Focus only on what you need for the formula!

M=m x v

M=10kg x 5 m/s=50 kg * m/s

Relative VelocityTRAVELING VELOCITY RELATIVE DIRECTION

SAME WAY add If going slower than you, direction is opp way you are going; If other object is going faster, direction=same way you are travelling

OPP WAYS subtract Always = same direction as other object

Newton's 1st Law: InertiaObjects in motion, tend to stay in that same path of

motion; objects at rest tend to stay at rest (unless outside forces act on them).

Ex: If you make a sharp turn in a moving car, things will tend to slide in the direction you were originally going.

Ex: If something is still, it won't spontaneously start moving unless a force is directed upon it.

Can anything move faster than the speed of light???

NO! This is a violation of the laws of physics!!!

What safety mechanisms are installed in vehicles to protect people in crashes?

Seat belts and air bags

How can we tell work has been done?

The motion of an object changes. If no change in motion, no work has

been done!

Where can one best observe the BEHAVIOR of matter?

In deep space, far from any star!

Potential Energy vs Kinetic Energy

PE=Energy stored (at rest) that gets converted to KE=Energy of motion.

So, if you do work on something, you are transferring stored (PE) energy into energy of movement (KE).