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physics midterm
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Gravity
Key Concepts:
Terms in this set (61)
What is the difference between distance and displacement?
Distance is scalar (only how far); displacement is vector (how far from start and direction)
What is the difference between velocity and speed?
Speed is scalar (how fast); velocity is vector (how fast and direction)
What is the slope on a position:time graph? Velocity:time graph?
velocity; acceleration
What could the signs of the velocity and acceleration be when:
* Object is speeding up? (+v, +a ; -v, -a)
* Object is slowing down? (+v, -a; -v, +a)
* Object is at constant velocity?
* Object is at rest?
-(+v, +a ; -v, -a)
-(+v, -a; -v, +a)
-(+v, a = 0; -v, a = 0)
- (v = 0, a = +/0/-)
When an object is at rest, the line on a position time graph is? Velocity time graph?
Flat line; flat line on 0 m/s
When an object is moving at a constant velocity, the line on a position time graph is?Velocity:time graph?
Straight sloped line (up or down); flat line above or below 0 m/s
When an object is speeding up, the line on a position time graph is? Velocity time graph?
Curved upward or downward getting steeper; sloped upward above 0 m/s, sloped downward below 0 m/s
When an object is slowing down, the line on a position time graph is? Velocity:time graph?
Curved upward or downward getting flatter; sloped back toward 0 m/s
Two cars are moving in a (+) direction. On a position time graph, how can you tell which car is moving faster? On a velocity:time graph?
The steeper slope is going faster; the line that is higher above 0 m/s
When do you know a car changes direction on a position time graph? On a velocity time graph?
The line changes from going up to down (or vice versa); line crosses 0 m/s
A bicyclist goes from 20 m/s to 10 m/s over a distance of 400 m. What is the acceleration of the bicyclist?
-.375 m/s2
A bottle rocket is shot up into the air at 65 m/s.How long is the rocket in the air?
13 s
What height does the rocket reach?
216 m
Which way does gravity always accelerate objects?
downward
Why is the horizontal velocity of a projectile always constant?
Object does not accelerate in the horizontal direction
What shape does a launched projectile take?
parabolic
What is the vertical acceleration of a projectile?
9.8 m/s2 downward
What is the horizontal acceleration of a projectile?
0 m/s2
If a bullet is shot at 100 m/s at an angle of 30 deg above the horizontal, how would you solve for:
H V
Horizontal velocity: 100 cos θ
Vertical velocity: 100 sin θ
If you travel 10 m north and then 5 m east, how far did you travel? At what angle did you travel from the starting point?
11.2 m; 26.6 deg east of north
A ball rolls off a 2 m counter at 10 m/s. How long is the ball in the air for? How far does the ball travel from the table?
0.64 s; 6.4 m
What is a force?
A push or a pull on an object. Creates the acceleration of the object
What is a field force versus a contact force? What are examples of both?
Field acts at a distance (gravitational, magnetic, electrical)Contact has to touch (normal, applied, tension, friction)
What is the unit for force?
Newton (N)
When do the following forces occur:Weight Normal Friction Tension Applied Air Resistance
Weight - when on earth (in a gravitational field),Normal - when on a surfaceFriction - when on a surface,Tension - when connected to a rope/string/wire,Applied - when physically pushed or pulled,Air - when object is moving through air
How do you calculate weight?
W = mg
What is the force pair that creates the force of weight?
Earth and the object
How are weight and mass different?
Weight changes with gravitational field, mass always stays the same
What direction does weight always point?
down
What direction does the normal force occur?
Perpendicular to surface
What is the force pair that creates the normal force?
Object and the surface
When will the weight and normal force be equal?
When the object is not accelerating moving up or down on the surface
When will the normal force be greater than the weight? Less than??
Normal force is greater when object is being pushed down into the surface more or the surface is accelerating upward under the object;Normal force is greater when object is being pushed down into the surface more or the surface is accelerating upward under the object
What the two types of friction?
Static and kinetic
Which type of friction is stronger and why?
Static, harder to make an object start moving
What are the three types of kinetic friction?
Fluid, sliding, rolling
What does the coefficient of friction tell us?
How rough or smooth the surface is
What is the formula for coefficient of friction?
u = Ff / Fn
How can we decrease friction?
Add wheels, lubricate, cushion of air
What is Newton's 1st law?
An object at rest/motion will stay at rest/motion unless acted upon by an outside force
Explain why a space ship will continue to move at a constant velocity in outer space after it shuts off its rocket boosters
No force is acting on the space ship
Why would a person fly out of a car if they do not have their seatbelt on and possibly rear end another car?
Their body will keep on moving because only the car's motion has changed/acted on
What is inertia?
The ability to resist a change in motion
What are the two factors that affect inertia?
mass and velocity
What is Newton's 2nd Law?
The net force on an object is equal to its mass times acceleration
What is the equation for Newton's 2nd law?
Fnet = ma
Using Newton's 2nd law, explain why a smaller object will accelerate faster than a larger object if the same force is applied to both objects.
Less mass means you need to have a larger acceleration to have equal net force
What is Newton's 3rd Law?
Every action has an equal and opposite reaction
Explain why an object cannot create a force all alone.
There has to be a reaction to an action force
If a horse is pulling a carriage, what can be said about the amount of force the horse applies to the carriage and the amount of force the carriage applies to the horse?
They are equal
When will your weight appear to increase/decrease?
Increase - you accelerate upwards;decrease - you accelerate downwards
When will your weight remain the same while you are moving? When will your weight be 0N?
Remain same - when you don't accelerate; 0 N - when you are in freefall
What are the tension rules?
Horizontal tensions are equal; vertical tensions add up to equal the weight
When will the tension in the wires increase?
When the wires become more horizontal
On an incline plane, how do you calculate the force that is pulling the object DOWN the incline plane? How do you calculate the force that is holding the object ON the incline plane?
Wx = mg sin Θ ;Wy = mg cos Θ
When is the normal force greater than the weight? Less than the weight?, on incline plane Equal to the weight? Object not being pushed up or down Equal to 0 N?
When pushing object downwards;Pulling upwards, object is hanging,Object not being pushed up or down not on surface
A 23.7 kg object is hung by two wires. Wire A is at an angle of 32 deg with a tension of 353 N. Find all other forces in the problem.
Fax = 299 N; Fay = 187 N; Fb = 302 N; Fbx = 299 N; Fby = 45 N; Θ = 8.6 deg; Fg = 232 N
You are pushing a 535 N lawnmower at an angle of 35 deg with 250 N of force. The lawnmower is accelerating at 2.5 m/s2. Find all forces involved.
Fx = 205 N; Fy = 143 N; Fn = 678 N; Ff = 68.5 N; Fnet = 136.5 N; u = 0.10; m = 54.6 kg
A kid is sliding down a 52 deg slide accelerating at 3.4 m/s2. If net force on the kid is 29 N, find all forces involved.
Fg = 83.3 N; Fgx = 65.6 N; Fgy = 51.3 N; Fn = 51.3 N; Ff = 36.6 N; m = 8.5 kg; u = 0.71
When an object is moving with uniform circular motion, which way does the net force point? Acceleration? center Velocity?
centerTangent to circle
Which of the following change while an object is moving with uniform circular motion:velocity/acceleration/net force? Justify your answer.
All change because you are changing direction constantly
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