Physics Midterm Study Flashcards
What is the definition of speed?
Speed is how fast an object is moving (the distance traveled every second).
How does speed differ from velocity?
Velocity requires a direction while speed does not; average velocity is calculated with displacement rather than with distance.
If a person runs with a constant speed of 4 m/s for 20 seconds, how far will they move?
d = st = 4 m/s * 20 s = 80 m
If a person runs with a constant speed of 5 m/s, how long will it take to move 1200 m?
t = ds = 1200 m / 5 m/s = 240 s
What is the definition of acceleration?
The rate at which the velocity of an object is changing.
If a motorcycle accelerates from rest with a rate of 7 m/s², what will its speed be after 3 seconds?
vf = vi + at = 0 + 7(3) = 21 m/s
If a motorcycle travelling at 45 m/s ‘forward’ suddenly accelerates ‘backward’ at 5 m/s², how long will it take to stop?
t = (vf - vi) / a = (0 - 45) / -5 = 9 s
What does the slope of a position vs time graph represent?
The slope of a position vs. time graph represents the object’s velocity.
What does the slope of a velocity vs time graph represent?
The slope of a velocity vs. time graph represents the object’s acceleration.
What is true about the acceleration rate of objects of different mass in freefall, ignoring air resistance?
All masses accelerate at the same rate.
How long does it take for an object to free fall (from rest) from a height of 50 meters?
t = √(2x/a) = √(2(50)/10) = 3.16 sec
If an object free falls (from rest) for 6 seconds, how far has it fallen?
x = vit + (1/2)at² = (1/2)(10)(6²) = 180 m
When an object is tossed straight upward, what is its velocity and acceleration at the peak of its motion?
Velocity at peak is zero; acceleration rate at peak is 10 m/s² downward.
What is inertia?
Inertia is the resistance an object has to changes in motion.
What is the quantity we use to measure inertia?
Mass.
What is a ‘force’?
A force is simply a push or pull on an object.
What is a ‘net force’?
Net force is the sum of all forces acting on an object (with directions taken into account).
State Newton’s 1st Law.
An object will remain in constant motion in the absence of a nonzero net force acting on it.
What does it mean for an object to be ‘in equilibrium’?
Equilibrium is the state of balanced forces, where the net force is zero.
What are the two states of motion possible for an object in equilibrium?
- At rest * Moving with constant velocity
State Newton’s 2nd Law in words.
The acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass.
State Newton’s 2nd Law as an equation.
a = F/m
What does it mean for two variables to be ‘directly proportional’?
If one variable increases, the other variable increases proportionally.
What does it mean for two variables to be ‘inversely proportional’?
If one variable increases, the other variable decreases proportionally.
If the net force acting on an object is doubled, what will happen to its acceleration rate?
It will double.
If the mass of an object experiencing a constant net force is suddenly doubled, what will happen to the acceleration rate?
It will be cut in half.
Distinguish between mass and weight.
- Mass: Amount of matter in an object, measured in kg. * Weight: Magnitude of the force exerted by the Earth on the object, measured in N.
If a person goes to the Moon, does their mass change?
Mass does not change.
If a person goes to the Moon, does their weight change?
Weight changes dramatically.
How do we calculate the weight of an object here on Earth?
W = Fg = mg
What is the weight of a 60 kg object here on Earth?
W = mg = 60 kg * 10 m/s² = 600 N
What is the mass of an object that weighs 750 N on Earth?
m = W/g = 750 N / 10 m/s² = 75 kg
An object experiences a forward force of 15 N and a backward force of 13 N. What is the net force on the object?
F = Ff - Fb = 15 N - 13 N = 2 N forward
A 3 kg object experiences a forward force of 25 N and a backward force of 13 N. At what rate will the object accelerate?
F = Ff - Fb = 25 N - 13 N = 12 N forward; a = F/m = 12 N / 3 kg = 4 m/s² forward
What is a ‘normal’ or ‘supporting’ force?
The force exerted by a surface on something being supported by that surface, always perpendicular to the surface.
What is momentum?
Momentum is the product of an object’s mass and velocity.
How do we calculate momentum?
p = mv
If the velocity of a mass triples, what happens to its momentum?
Momentum also triples.
What is impulse?
Impulse is the product of a force and the time during which it acts.
How do we calculate impulse?
J = Ft
What is true about the impulse and change in momentum?
Impulse is always equal to the change in momentum.
Under what condition is the momentum of a system conserved?
There is no impulse acting on the system (meaning no net force).
What is recoil?
The backward velocity given to an object when it shoots another object forward.
How does a rocket accelerate in outer space?
By pushing exhaust gases out the end of the rocket.
What is the difference between ‘revolution’ and ‘rotation’?
- Revolution: Moves around an external object (e.g., Earth around the Sun). * Rotation: Spins on its axis (e.g., Earth spinning on its axis).
When an object moves in a circle, what is the angle between the velocity vector and the acceleration vector?
90° (perpendicular).
What happens to the acceleration of an object in uniform circular motion if the object’s speed doubles but the radius stays constant?
The acceleration would quadruple.
What did Newton discover about gravitation?
Gravitation is universal and directly proportional to the masses of the objects.
What is the angle between the velocity vector and the acceleration vector in uniform circular motion?
90° (perpendicular)
If an object’s speed doubles while its radius stays constant, what happens to its acceleration?
The acceleration quadruples (becomes four times more)
What happens to the acceleration if the radius is doubled while speed remains constant?
The speed is cut in half (becomes two times less)
What did Newton discover about gravitation?
Gravitation is universal and directly proportional to the masses of the objects and inversely proportional to the square of the distance between them.
Write Newton’s Law of Universal Gravitation formula.
Fg = Gm1m2/d²
If the distance between two masses doubles, what happens to the gravitational force between them?
The force is quartered (four times less)
What happens to the gravitational force if the distance triples?
The force is one-ninth as much (nine times less)
What happens to the gravitational force if the distance is cut in half?
The force is quadrupled (four times more)
When a 600 kg object and a 5 kg object attract each other gravitationally, which object experiences the greater amount of force?
They both experience the same force!
If a person climbs a very tall ladder to a height equal to one Earth radius, how does their weight change?
Their weight would be four times less (one quarter as much)
What is the value of G, and what does this small value indicate about the strength of gravity?
6.67 x 10⁻¹¹, indicating that gravity is very weak compared with other fundamental forces.
What is a ‘gravitational field’?
A field of attraction surrounding any mass, stronger at points closer to the mass and weaker at points farther from the mass.
What does Kepler’s 1st law say about the paths of planets as they orbit the Sun?
A planet orbits in an ellipse with the Sun at one focus point.
What does Kepler’s 2nd law state?
A planet orbiting the sun sweeps out equal areas in equal times.
What is Kepler’s 3rd Law?
The square of the period of a planet’s orbit is proportional to the cube of its orbital distance.
How does a planet’s average distance from the Sun affect its period?
Planets that are further from the Sun have longer periods.
At what point in a planet’s elliptical orbit around the Sun is potential energy greatest?
At aphelion (farthest from the Sun)
At what point is kinetic energy greatest in a planet’s orbit?
At perihelion (closest to the Sun)
How do we calculate the work done on an object by a force?
Work is force multiplied by distance. W = Fd
What work does a woman do on a box if she pushes it 5 meters with a force of 200 N?
W = 200 * 5 = 1000 J
Under what circumstances is work positive?
When force and distance point in the same direction.
When is work negative?
When force and distance point in opposite directions.
When is work zero?
When there is no distance, no force, or if the force and distance are perpendicular.
When an object is lifted upward, does the force exerted by Earth do positive or negative work?
Negative work.
When an object falls, does the force exerted by Earth do positive or negative work?
Positive work.
What is the net work done on a crate pushed with a 100 N force against 80 N of friction over 6 meters?
120 J
How much work does a waiter do on a tray of food while moving at constant speed?
Zero.
How much work does a weightlifter do on a 15 kg dumbbell raised 2 meters?
300 J
What is the definition of power?
The rate at which work is done. P = W/t
How much work does a 60 kg girl do to raise her body 5 m in 8 seconds?
2500 J; Power output is 312.5 W
If the same girl runs up the same stairs in 4 seconds, how does her power output compare?
Her power output will increase.
What is the power output of a machine that does 5000 J of work in 30 seconds?
166.7 W
What is kinetic energy and how do we calculate it?
Energy associated with motion. KE = (1/2)mv²
Can kinetic energy ever be negative?
No.
If an object moves twice as fast, by what factor has its kinetic energy changed?
Four times more.
If the net work done on an object is positive, what happens to its kinetic energy?
KE will increase.
If the net work done is negative, what happens to kinetic energy?
KE will decrease.
If the net work done is zero, what happens to kinetic energy?
KE will not change.
What is gravitational potential energy and how is it calculated?
Energy associated with position (height). PE = mgh
Can gravitational potential energy be negative?
Yes, if below the reference level.
If a ball is dropped from rest, how do its PE and KE compare just before it strikes the ground?
They are equal (conservation of energy).
What is total mechanical energy?
The sum of potential and kinetic energy.
What happens to a bullet’s PE and KE as it rises?
PE increases while KE decreases; KE is zero at maximum height.
When an object experiences friction and air resistance, is total mechanical energy conserved?
No, it reduces TME.
Where does the ‘lost’ energy from friction and air resistance go?
Converted to thermal energy.
What is the definition of Work?
The product of force and distance.
What is the abbreviation for Power?
P
What is the unit for Kinetic Energy?
J
What is the abbreviation for Gravitational Potential Energy?
Ug
What is the unit for Total Mechanical Energy?
J
