Midterm review

Mostly concepts, with a few calculations thrown in for flavor

Chapter 1 - Units

• What are the three base units we use in this class for distance, time and mass?

• Meters, seconds, kilograms• Do we ever use centimeters or grams?• NO, we do not• Why Not?• Because, Dr. Mason, doing so would make all

of the other derived units (such as Newtons and Watts) come out all wonky.

Ch. 1 - Conversions

• How many centimeters in a meter?• How many meters in a kilometer?• How many seconds in a minute?• How many seconds in an hour?• How many degrees in a revolution (circle)?

Trig Review - 1

• Define sin(θ)• Define cos(θ)• Define tan(θ)• Find all three for the triangle below

θ4

35

Trig Review - 2

• In terms of F and θ, FX = ?

• In terms of F and θ, FY = ?• A force F = 13 N is directed at an angle θ = 400

above the horizontal. • Find FX

• Find FY

Trig Review - 2

• If I know that the x-component of a force is 4 N and the y-component of a force is 7 N, how will I find the magnitude of the overall force?

• So then do that.• How will I find the angle at which the force is

directed?• So then do that too.

Trig Review - 4

• Which of the following are vector quantities and which are scalar quantities:– Force– Acceleration– Mass– Velocity– Speed– Time– Weight

Trig Review - 5

• For the vector quantities in the previous slide, is there any difference in how you determine the magnitude or angle (direction) if you have the x- and y- components?

• This page is too easy. Whoever you are, you get to do the next slide, too. Everyone else in the room, cheer for this person for being so lucky.

Everyone’s favorite problem.• Little Joey is once again adrift on his sad, sad

little raft. He knows you hate him and his raft, but begs of you to find his resulting acceleration anyway. The wind is acting due east and pushes with 20 N and the current is at 350 and pushes with 30N. Raft and Joey have a mass of 200 kg. Find Fx, Fy, F, θ, and a.

The Wile E. Coyote Problem

• Just kidding. • Instead, resolve these vectors and find the

resultant magnitude and direction of the acceleration if the mass is 5 kg.

4

3

4 8

1-D stuff• What is the difference between velocity and

acceleration?• Using your notes/friends, find the following:– Equation relating distance, time and acceleration

but not speed– Equation relating distance, time and speed but not

acceleration– Equation relating speed, time and acceleration but

not distance– Equation relating distance, speed and acceleration

but not time

More 1-D stuff

• Define ΔV• Define ΔX• What is negative acceleration?• What is negative velocity?• In general, why do we say that g = -9.8m/s2

instead of 9.8m/s2 ?

2-D stuff• For projectiles, in which direction is motion

constant and in which is it changing? • Why are they different?• On the arc below, draw the directions of the

velocity and acceleration vectors in 5 places.

More 2-D stuff

• As a convertible drives along, the passenger throws a rock vertically upward. Ignoring air resistance, where will it land?

• Why?• At what point in the trajectory was the rock

moving the slowest?• Why?

More 2-D stuff

• A ball is dropped from a height H at the same instant an identical ball is thrown horizontally with speed V0 from the same height. Which hits the ground first? Which has a larger velocity?

• Explain all that.

More 2-D stuff

• Okay, we’re going to revisit the football punter problem. V0 = 18 m/s, = 290.

• What info do you use to find the range?• What info do you use to find the height?• What info do you use to find the time of

flight?

Forces

• Write out Newton’s 3 laws. Full sentences, not just the names.

Forces continued

• What is the difference between weight and mass?

• If all the forces acting on an object = zero, is the object definitely not moving? Why or why not?

• What do you call it when all the forces on an object = 0?

Forces continued

• Two high school students push to the right on a stalled car. Their individual forces are 340 N and 280 N. There is a frictional force of 450N acting on the car. What is the net force acting on the car?

• If the car’s mass is 1200 kg, what is the car’s acceleration?

Forces continued

• A man and a moose are standing in the middle of a frictionless frozen lake. The man’s mass is 90kg, the moose’s mass is 400 kg. The man pushes on the moose with a force of 110N. What is the moose’s force on the man?

• What are the individual accelerations?

Forces continued

• What is the difference between g and G?• What are the values of g and G (including

units)?• When do you use each (MAKE SURE YOU

KNOW THIS)?• How do you find the acceleration due to

gravity at the surface of any planet?

Forces continued• What is the equation for static friction?• Of static or kinetic friction, which one varies?• Of static or kinetic coefficient of friction, which

one is usually larger?• Describe the two step process for solving the

classic “a 10 kg block with coefficients of static and kinetic friction of 0.43 and 0.37 is pushed on by a force of…” problem.

Forces continued

• In general, ΣF = ?• What are the conditions for equilibrium?• What is your general strategy for solving the

classic “two ropes pull in such and such direction, what direction does the third rope have to pull” kind of problem?

Circular stuff

• What is the equation for the circumference of a circle?

• So, if speed = distance/time, what is the equation for speed in a circle?

• Find the equation for centripetal acceleration• Find the equation for centripetal force• Okay, that’s enough circular motion.

Energy and Work

• What is the formula for work?• What is the formula for kinetic energy?• What is the work-energy theorem?• What is the formula for gravitational potential

energy.• Explain where this equation for PE comes

from.

Energy and Work

• You have a problem in which the total mechanical energy is conserved. Write out explicitly the entire equation you would use to solve for some quantity (say, the final speed) and explain this equation to me so that i’m convinced you understand it.

• In what kind of case is total mechanical energy not conserved?

Energy and Work

• Explain the difference between conservative and nonconservative forces.

• Give examples of each.• What is the formula for power?• Explain the relationship among power, work

and energy.