Transcript P2.2_-_Speeding_up_and_slowing_down_answ... 309KB Jun 06

Speeding up and
slowing down - Answers
f = ma
Terminal velocity
1. What are the four forces acting on an aeroplane. Thrust, drag,
lift, weight.
2. How do each of the four forces act on an airplane in flight?
(Which direction does each force push or pull on the airplane
in flight?)with motion, against the motion, upward, downward
3. Which force on an airplane is always directed toward the
centre of the earth? weight
4. Which force is responsible for moving the airplane forward?
thrust
5. Which force do the wings of the airplane generate? lift
For questions 7-10, predict what effect the following flight
conditions would have on the plane. (Would the plane rise,
fall, slow, or accelerate?)
7. Drag > Thrust slow down (decelerate)
8. Lift > Weight rise
9. Thrust > Drag accelerate
10. Weight > Lift fall
11. Define balanced and unbalanced. Balanced – when all the
forces acting on an object are equal. Unbalanced – when the
forces acting on an object are not equal.
12. During a flight when we are cruising at a specific altitude, the
four forces are balanced. At which points during a flight are the
forces unbalanced? Take off, climbing to cruising altitude,
descending to land, landing.
13. Define Newton's First Law of Motion. An object will stay at rest
or continue at a constant velocity unless acted upon by an
external unbalanced force
14. In your own words, explain how Newton's First Law of Motion
explains the motion of a cruising airplane. The plane will stay
cruising at a constant speed and height unless another force
acts upon it when a change in direction or speed will take
place.
Force, mass, acceleration
The diagram shows an athlete accelerating.
The athlete has a mass of 65 kg and produces a constant forward
force of 364 N.
(i) Write down the equation that links acceleration, force and
mass. F = ma
(1 mark)
(ii) Calculate the maximum acceleration of the athlete.
Show clearly how you work out your answer.
(2 marks) a = F/m = 364/65 = 5.6m/s2
(b) The athlete’s forward force is the same throughout the race.
Explain why the acceleration of the athlete decreases to zero
during the race. As the forward velocity increases the air
resistance also increases and eventually the forces will be equal.
(2 marks)
1. A car accelerates from 0 m/s to 10 m/s in 50 seconds. What is
the acceleration?(a=(v-u)/t) a=10/50=0.2m/s2
2. A train decelerates from 30 m/s to 25 m/s in 2 minutes. What
is the acceleration? (Answer to 2 s.f.) (a=(v-u)/t)
a=5/180=0.042m/s2
3. A car of mass 900 kg has an engine which exerts a force of
450N on the car. Assuming 100% efficiency, what is the
minimum amount of time needed for the car to accelerate from
0 to 10 m/s? (f=ma) a=450/900=0.5 (a=(v-u)/t) t=10/0.5=20s
Terminal Velocity
0 seconds
10 seconds
Fair =
400N
Fweight =
F
weight
1000N
Fweight =
1000N
20 seconds
Fair =
800N
Fweight =
1000N
30 seconds
Fair =
1000N
Fweight =
1000N
1. Define the term terminal velocity. The velocity reached when
all forces acting on an object are balanced
2. In each of the above diagrams what is the resultant force? A
1000N Down, B 600N Down, C 200N Down, D 0N Down.
3. Given that the acceleration of the parachutist is constant
within all of the time frames, plot a speed time graph for the
parachutist. (Use the graph paper over the page)
320
(294)
280
240
200
160
120
80
40
0
10
20
Time (s)
30
40