Download 8th 2014 midterm

8th 2014 midterm Review Key
1) What is displacement? The difference between the initial and final positions of an
object.
2) Motion means you are changing what? Position
3) If you have a point used to locate a thing, what is it called? A reference point
4) Total distance traveled divided by the total time of travel gives you what? Average
speed
5) What is shown in this graph? An object whose speed is increasing at a steady rate
over time.
6) if a ball rolls for 10 seconds and rolls 5 meters, what is its average speed? 0.5 m/s
7) If an object is at rest, what is its speed? 0 m/s
8) What does acceleration describe? How velocity changes with time
9) What does instantaneous speed mean? The speed at any instant in time
10) What two things do you need to know to describe velocity? Speed and direction
11) A straight horizontal line on a speed-time graph says what? The change in speed is
zero
12) A car slows down. Is it accelerating? Yes, it has a negative acceleration.
13) An object is moving at a constant speed. What would a distance-time graph show? A
straight diagonal line
14) Is gravity a contact force or a noncontact force? Noncontact.
15) If an arrow represents a force, what does the length of the arrow show? Strength of the
force
16) How is momentum affected by mass? A more massive object has more momentum.
17) If an object is accelerating, what is it doing? Changing speed or changing direction
18) Is friction a force? You betcha!
19) We walk forward because the ground is doing what? Pushing on us
20) Action and reaction forces are equal, but act in --- directions. Opposite
21) Daniel hits a nail with a hammer. What object(s) get a force? Both the hammer and
the nail
22) What is p = m x v? The equation for momentum
23) How does the combined momentum of two objects before a collision compare to their
combined momentum after a collision? They are the same
24) Define balanced forces. Forces that are equal in size but opposite in direction acting
on the same object
25) What is static friction? The force you have to overcome to start an object moving
26) I am falling. What upward force is acting on me? Air resistance
27) If a 3,000-N force give something an acceleration of 30 m/s/s, what is the object’s
mass? 100 kg
28) State Newton’s 3rd law. For every action, there I an equal and opposite reaction.
29) What is the unit:
a) of force? Newtons
b) of work? Joules
c) for power? Watts
30) What force is the result of using a machine? Output force
31) How does a machine change the type of a force? It doesn’t. It can’t. Ain’t happening.
32) A carpenter applies 150 N to the end of a crowbar. The force exerted on the board is
600 N. What is the mechanical advantage of the crowbar? 4
33) A worker applies a force of 25 N to pry open a window that has a resistance force of
500N. What is the mechanical advantage of the crowbar? 20
34) Find the force needed to lift a 2000N rock, using a jack with a mechanical advantage
of 20. 100N
35) Joe is using a crowbar to remove a tree stump. He applies 2056 J of work to the
crowbar. The output work of the crowbar is 514 J. What is the efficiency of the
crowbar? 25%
36) What is the ideal mechanical advantage of the pulley shown? 2
37) How do you calculate the mechanical advantage of a wedge? Length / height
38) What’s a compound machine? Two or more simple machines working together.
39) A wheelbarrow is an example of a compound machine that uses a lever and a wheel
and axle. The efficiency of a compound machine is calculated by multiplying the
efficiencies of each simple machine together. Suppose the efficiency of the lever is
96% and the efficiency of the wheel and axle is 93%. What is the efficiency of the
wheelbarrow? 0.96 x 0.93 = 0.89(ish)
40) Define inclined plane. A slanted surface used to raise an object
41) Define lever a bar that is free to pivot about a fixed point
42) What word describes the rate at which work is done? Power
43) Define mechanical advantage. The amount by which a machine multiplies an input
force.
44) If you wrap an inclined plane around a cylinder, what do you get? A screw
45) Define compound machine. Two or more simple machines working together.
46) What is:
a) a measure of the distance an object travels in a unit of time? Speed
b) An object’s distance in a certain direction from a reference point. Position
c) The rate of change of position in which the same distance is traveled each
second. Constant speed
d) A change in the velocity during a time interval divided by the time interval
during which the velocity changes. Acceleration
e) The speed and the direction of a moving object. Velocity
f) The total distance traveled divided by the total time taken to travel that distance.
Average speed
g) The process of changing position. Motion
47) Describe the motion of a car with an acceleration of –2 m/s2. The car is slowing down
2 m/s every second
48) "If no forces are acting on a moving object, it will eventually come to rest." Is this
statement true or false? Discuss your reasons for thinking this way.
49) Scissors are basically two first-class levers. Using what you know about calculating
mechanical advantage for levers, explain why it would be easier to cut something if the
handles were long and the blades were short.
50) A swimmer swims 20 m in 40 s. What is the swimmer’s average speed? 0.5 m/s
51) You travel 190 km in 2 h. What is your speed in km/h? 95 km/hr
52) A car goes from 80 km/h to 20 km/h in 0.5 h. What is the acceleration in km/h2?"
-120 km/hr
53) A top-fuel dragster accelerates from rest to a velocity of 100 m/s in 8 s. What is the
acceleration? 12.5 m/s/s
54) A train traveled 250 kilometers (km) from its starting point in 5 hours (h). If the train
continues at the same average speed for another 4 hours, how far will it have traveled
from its starting point? Show your work. 450 km
55) Suppose that the average speed your dog can run is 2 m/s. Remember, average
speed = total distance/total time. How much time will it take your dog to run 120 m? 1
min
56) Calculate the force on an object that has a mass of 12 kg and an acceleration of 4
m/s2. 48 N
57) How much power is needed to do 1,000 J of work on a box if it takes 50 s to lift it?
20W
58) How much work is done if 500 W of power is used over 2 min? 60,000 J