Describing Motion
What is a reference point?
The place from which you measure/observe motion.
What is the equation for speed?
s = d/t
Name 3 ways an object can accelerate.
speed up, slow down, change direction
State Newton's 1st Law.
object stays at rest/constant velocity until a net force acts.
What is terminal velocity and when does it occur?
max velocity of a falling object; occurs when gravity and air resistance balance (net force = 0).
Distance vs. displacement — which includes direction?
displacement
What's the difference between average and instantaneous speed?
average = total d ÷ total t; instantaneous = speed at one moment.
Write the acceleration equation and define each variable.
a = (v_f − v_i)/t.
a=acceration
v_f= final velocity
v_i= initial velocity
t= time
Define net force and give the net force of 5 N left + 2 N right.
3 N left.
sum of all the individual pushes and pulls acting on an object.
Write the momentum equation and what each letter stands for.
p = mv
p=momentum
m=mass
v= velocity
A runner circles a 400 m track. What is her displacement?
A girl runs 3.1 mi in 0.5 hr. Find her average speed
6.2 mi/hr
A car goes 35 km/hr → 45 km/hr in 0.25 hr. Find a.
40 km/hr²
State Newton's 2nd Law and write its equation.
F = ma
The force acting on an object is equal to the mass of that object multiplied by its acceleration
Find the momentum of a 1300 kg car moving 28 m/s.
6,400 kg·m/s.
A truck drives 4 mi West then 6 mi North. Find distance AND displacement.
400 — d = 10 mi; Δx = √(16+36) ≈ 7.21 mi NW.
A car travels 0.75 hr at 45 mi/hr. How far does it go?33.75 mi.
33.75 mi.
A jet at 80 m/s stops in 10 s. Find a.
−8 m/s²
Name the 3 types of friction and give an example of each.
static, sliding, rolling.
State Newton's 3rd Law
Every action has an equal and opposite reaction;
A car travels 155 miles south turns and then drives 350 miles east, this took the car 8 hours to complete. What is the velocity, distance, displacement, and acceleration assuming the car started setting still?
Distance: 505 miles
Displacement: 383 miles southeast
Velocity: 63.125 mi/hr
Acceleration: 7.89 mi/hr ^2
What does it mean that "speed can be constant but velocity changes"? Give an example.
Direction changes (e.g., a car turning a circle at constant speed).
On a velocity vs. time graph, what does the slope represent? What does a flat line mean?
slope = acceleration; flat line = 0 acceleration (constant velocity).
A 42 kg suitcase — find its weight. Then explain how its weight changes on the Moon. Remember the number we use for gravity. Your answer needs to be in NEWTONS.
F = (42)(9.8) = 411.6 N; on the Moon, weight ≈ 1/6 (mass never changes).
State the Law of Conservation of Momentum
Momentum is never created or destroyed, only transferred.