Physics Intro
Express the following in scientific notation:
a. The power output of the Sun (393,000,000,000,000,000,000,000,000 Watts):
3.93 β 10^26 π
We determined that a trip from lower Calvert County, MD to SU takes about 3 hours, and due to
the unique geography of Maryland, you travel a distance of 227 km while your displacement is
72.58 km east. Calculate average speed and average velocity of this trip.
average speed: 76 km/hr
average velocity: 24 km/hr east
A ball is dropped from a height of 15 m. What is the ballβs velocity when it reaches the ground?
οΏ½Vπ¦ β β17.1 m/s
An 8 kg box is pushed by a mole rat on a perfectly smooth and slippery surface. The mole rat is
exerting a force of 1.2 N in the positive x direction.
a. What is the acceleration of the box?
b. What is the velocity of the box after 21 seconds?
a. 0.15 m/s^2
b. 3.15 m/s
You are on a 3 m diameter Merry-go-round that is completing one full rotation every 20
seconds. Despite everyoneβs advice you refuse to hold on and your mass is 70 kg. Calculate
the following:
a) your speed
b) your acceleration
c) the net centripetal force acting on you
d) What physical force is providing the net centripetal force acting on you?
a) 0.47 m/s
b) 0.148 m/s^2
c) 10.4 π toward the center of the merry-go-round
d) A sketch of you would show that the only object you are touching is the merry-go-round. Since
you are not holding onto it the force providing the centripetal force must be the static friction
between your shoes and the merry-go-round.
What is the difference between a law and a theory?
A law is little more than a summary of observations. βWhen this occurs, that occurs next.β
A theory explains why something happens and provides understanding. βBecause of
EXPLANATION this will happen.β
Fred is on a perfectly circular track with a circumference of 100 m. Fred runs at a pace of 2.5 m/s.
After running for 40 s, what is Fredβs distance travelled, magnitude of displacement, average
speed, and magnitude of average velocity?
Traveled 100m
Velocity is 0 m/s
A car sitting at a stop light can accelerate at 3.2 m/s2.
a. How long after the light turns green will the car be moving at the speed limit of 40 km/hr?
b. How far has the car travelled during this time period?
A. 3.47 s
B. 19.3 m
You have a mass of 75 kg and are standing in an elevator. The elevator is exerting an upward
force on you of 600 N. What is your acceleration?
-1.8 m/s^2
You are designing a roller coaster that needs to complete a full loop. The radius of the loop is 25
m. What is the minimum speed the roller coaster car must have at the top of the loop in order
to stay on the track?
15.7 m/s
Evaluate: (6 π/π ) β (2 π /ππ)
12 m/kg
Answer the following questions based on the motion diagram below.
a. During what time interval(s) is the object moving most quickly?
b. What does it mean that the spots representing the location of the object from 0 s to 3 s are
equally spaced?
c. When is the object going faster, at 4 s or at 7 s?
a. The object is moving most quickly from 3 to 6 s. The distance between the dots is larger in that
time interval indicating the object is moving faster
b. The object is moving at a constant velocity. Each second it travels the same distance so the dots
end up the same distance apart.
c. The distance between the 4 s dot and its neighbors is larger indicating that the object is moving
faster at 4 s.
A car is moving at 25 m/s at an angle of 42Β° left of the y-axis. What are the x- and y-
components of the carβs velocity
Vx = -16.7 m/s
Vy = 18.6 m/s
You are pulling a 25 kg suitcase behind you via an attached string that is at an angle of 38Β° above the horizontal. You are pulling on the string with a force of 73 N. What is πΉπΊπππ’ππ ππ ππ’ππ‘πππ π?
200.1 N
A child with mass 25 kg is standing at the edge of a 2 m radius merry-go-round that is rotating at
π = 0.84 πππ/π . The child is not holding onto anything.
a) What is the net centripetal force that must be acting on the child to keep them in uniform
circular motion? What direction is it
35 N towards the center of the circle
Convert 120 (kg^2 * m)/s to (g^2 *cm)/ day
1.0368 * 10^15 (g^2 *cm)/ day
For each scenario, explain why it is or isnβt possible, and give an example if it is
a. Can an object simultaneously have a velocity of zero and an acceleration that is nonzero?
b. Can a car traveling west be simultaneously accelerating to the east?
c. Can an objectβs speed be decreasing in if its acceleration is positive?
d. Can an object be increasing in speed as its acceleration decreases in magnitude (size)?
a. Yes. Acceleration can only tell you how velocity is changing. It cannot tell you anything about
what the velocity is. Example: throw an object straight up into the air and it will slow down.
At its peak height it will have zero velocity but will still be accelerating downward as evidenced
by the fact that it does not stay at that height forever.
b. Yes. Acceleration can only tell you how velocity is changing. It cannot tell you anything about
what the velocity is. Example: moving to the West at 20 m/s and slowing down. Accelerating
to the East in this case will slow the vehicle but it will still be travelling west (until it comes to
a stop).
c. Yes. Acceleration can only tell you how velocity is changing. It cannot tell you anything about
what the velocity is. Example: moving to the West at 20 m/s but slowing down β with East
being defined as the positive direction.
d. Yes. Acceleration can be decreasing but still be in the direction of motion. Example: Moving
East at 10 m/s and accelerating at 5 m/s2 east. The next second your speed is 15 m/s but your
acceleration is now 2 m/s2 east. The next second your speed is 17 m/s. You speed is higher
now than it was even though your acceleration is decreasing in magnitude
You are slowly falling to the ground with a parachute at a rate of 2.5 m/s. When the tennis ball
you are holding is 50 m from the ground you toss it up into the air with a speed of 9 m/s with
respect to you.
a. How long before you does it hit the ground?
b. How fast is the tennis ball moving when it hits the ground?
a. 16.07 s
b. -32.0 m/s
You place a 3 ππ rock on a 34Β° incline. The coefficient of static friction between the rock and the incline is 0.4. The coefficient of kinetic friction is 0.22. The rock slides down the incline. What is the magnitude and the direction of the friction acting on the rock?
5.36 N up the Ramp
How fast must you drive your car over a roughly circular hill of radius 20 m for your apparent
weight to be half your actual weight?
9.90 m/s
Speed limit signs in the US are expressed in units of miles per hour (mi/hr), but most equations
we use in this class require quantities to be in SI base units. What is the typical highway speed
(65 mi/hr) in meters per second (m/s)? (1in = 2.54cm)
29.06 m/s
Draw a plausible motion diagram for a car approaching a light that has just recently turned red.
Once the light turns green the car accelerates back up to 15 m/s. Now draw corresponding
position vs. time, velocity vs. time, and acceleration vs. time graphs
Answer on board
A long jumper is running at 10 m/s on a concrete track when she jumps at an angle of 23Β° above
the horizontal.
a. Assuming her jump does not alter her horizontal velocity how far does she jump?
b. What is the maximum height attained by the long jumper?
The maximum height of projectile motion occurs when π£π¦ = 0
a. x = 8.66 m
b. 0.919 m
You place a 6 ππ book on a 25Β° incline. The coefficient of static friction between the book and the incline is 0.3. The coefficient of kinetic friction is 0.18. Describe the motion of the book.
2.54 m/s^2
a. How large must the coefficient of static friction be between the tires and the road if a truck is
to round a level curve of radius 150 m at a speed of 35m/s?
b. At what angle would the curve need to be banked for the car to navigate the curve safely
without friction?
a. 0.83
b. 39.8 degrees