Module 1
What is the difference between a vector and scalar quantity?
Direction is included in a vector quantity
What is air resistance? How does it affect falling objects?
The tendency of molecules of the gases in the atmosphere to resist the motion of objects through them. It slows falling objects down, but is minimal with heavy or aerodynamic objects.
From where do we measure the angle of all vectors?
the positive x-axis
What is the shape of the path of a projectile?
arc, parabola
What is a normal force?
The force of a surface holding an object up.
What is required for an object to be in translational equilibrium?
The sum of the forces acting on the object are zero (no motion or constant acceleration)
What is centripetal force?
the force needed for an object to move in a circle, a force directed toward the center of a circle
What is the Law of Conservation of Energy? (aka the 1st Law of Thermodynamics)
Energy cannot be created or destroyed. It can only change form.
Which is a vector quantity: speed or velocity?
velocity
If a ball is thrown up in the air, where is its velocity zero? When its velocity is zero, what is it acceleration?
at the highest point
-9.8 m/s2
If a vector has an x-component that is negative and a y-component that is positive, which quadrant of the coordinate plane does it fall in? If we calculate the angle of the vector, what will we have to do to ensure the angle is defined properly?
Q2
+180
What do we know about the x- and y- components of a projectile's acceleration when the projectile is at its maximum height?
Its x-component is the zero throughout its trajectory. The y-component is the acceleration due to gravity.
State Newton's 3 laws.
1. Object in motion/rest tends to stay in motion/rest until acted upon by an outside force.
2. F = ma
3. For every action, there is an equal and opposite reaction.
What is required for an object to be in rotational equilibrium?
The sum of the torques equals zero.
What is centrifugal force?
a fictional force directed out of the circle
What is the difference between work and energy?
What is the same?
They both use Joules as units.
What information does the slope of a position vs. time graph give us?
velocity
A ball is thrown up in the air with an initial velocity of +1.5 m/s. If it is caught at exactly the same height from which it was thrown, what will its velocity be?
-1.5 m/s
See the figure from #8 on p. 103. Which object is accelerating more quickly?
object #2, B
What happens to the y-component of a projectile's velocity as it travels through the air?
It is upward, but decreasing until the mid-point. Then it increases again in the downward direction.
If you are given two friction coefficients for an object on a surface 0.25 and 0.35, which is likely to be the static coefficient and which is the kinetic coefficient?
static 0.35
kinetic 0.25
When analyzing a block sliding down an incline, how do we split up the components of the forces with relation to the incline? Why?
parallel and perpendicular to the incline
because most of the forces are already in those two directions
An object moves at a constant speed. Is the acceleration necessarily zero? Why or why not?
No, the direction could be changing, so the acceleration would not be zero.
A roller coaster rests atop a 113 m high hill. It begins to roll down the hill and back up to the top of another hill which is 67 m high. Ignoring friction, what is its speed at the top of the second hill?
30 m/s
What information does the slope of a velocity vs. time graph give us?
acceleration
A car traveling 25 m/s stops in 103 m. What is the acceleration provided by the brakes in m/s2?
-3.0 m/s2
See the figures from #8 & 9, p. 103
Which object is speeding up?
object #1
What two conditions are required to use the range equation?
1. Height of the landing must be the same as where it was launched.
2. g is positive
If a box weighs 1,234 pounds on earth, what will its weight be on the moon? The acceleration due to gravity on the moon is 5.3 ft/s2.
210 pounds
A mechanic is exerting 97 Nm of torque on a nut and is applying a 415-N force perpendicular to the wrench. How far away from the center of the nut is he grasping the wrench?
0.23m
A child swings a 0.345 m string with a 0.015 kg ball around his head. He twirls it faster and faster. When the ball reaches 12.1 m/s, the string breaks. What is the maximum force of tension the string withstood?
6.37 N
If an object has an acceleration of 1.4 m/s2 but a velocity of -12.6 m/s, is the object speeding up or slowing down at that instant?
slowing down
A student drops a rock off a cliff. If the rock takes 3.5 seconds to reach the bottom of the cliff, how tall is the cliff in meters?
60 m
The velocity vector of a car has an x-component of 17 m/s and a y-component of -11 m/s. What are the magnitude and direction of the velocity vector?
20 m/s @ 327
What is the range of a cannon that fires its cannonballs with an initial velocity of 350.0 ft/s at an angle of 35˚?
3600 feet
A 314-pound rock is blocking the road with a µs=0.45 and a µk=0.32. What is the magnitude of the force the man must overcome to start moving the rock?
140 lbs
Two children are on a seesaw. If the boy weighs 352 N and sits 1.12m from the fulcrum, how much does the girl weigh if she must sit 1.34 m from the fulcrum to achieve balance?
294 N
A car is traveling down a slippery road (µ=0.22). What is the maximum speed at which the car can take a flat curve whose radius of curvature is 13.4 m?
5.4 m/s
See the graph on p. 563
a) At approximately what times does the car change directions?
b) During which time intervals is the car moving the fastest?
a) 2, 7.6, 16 sec
b) 11-12 sec
Tell the steps to solve Practice Problem 6, p. 104
1. Break each vector into its x- and y-components.
2. Add the x-components together. Add the y-components together.
3. Find the magnitude of the new vector.
4. Find the angle of the new vector. Determine what quadrant it is in and add 180 or 360, if necessary.
A 30.1 kg block of wood slides down an incline angled at 23˚. If friction is ignored, what is the block's acceleration?
3.8 m/s2
See the graph on p. 564
a) During which time intervals is the acceleration equal to zero?
b) What is the acceleration at 13 sec?
a) approx. 4.0-7.1 sec, and 16.3-16.7 sec
b)1.0 m/s2