Download sph 3u(g) test: dynamics

SPH 3U(G) MOCK TEST: DYNAMICS
Mr. Moors
1.
Define mechanics, force, Newton and inertia.
2.
Fill in the blanks.
Newton's __________ Law. Every __________ continues in its state of ______, or ____________ motion in a
___________ line unless acted upon by an ________________ force. [1st, object, rest, uniform, straight, unbalanced]
Newton's __________ Law. When an ________________ force acts on an ____________, the object will ____________
in the _______________ of the unbalanced force. The acceleration of the object is directly _______________to the size
of the_____________ and inversely proportional to the________ of the object. [2 nd, unbalanced, object, accelerate,
direction, proportional, force, mass]
Newton's __________ Law. If object A exerts a force on object B, then object B exerts a force equal in magnitude but
opposite in direction on object A. These two forces are called _____________________ pairs. [3 rd, action reaction]
3.
State the four fundamental forces briefly describe them and state which is the strongest and which is the weakest.
(3) [gravitational, weak, strong, electromagnetic]
4.
State two examples of inertia that are dangerous. State two examples of inertia that are beneficial. [many
solutions]
5.
a) State one similarity and two differences between an action force reaction force pair. [magnitude; direction,
object acted on]
b) State the reaction force pair to each force stated below.
i) Jackie pulls eastward on a rope attached to a wall.
ii) Gravity pulls downward on a toy attached to a string which is attached to the ceiling.
iii) The normal force of the ground pushes Bob up.
iv) Jenny pulls one end of an elastic band downward.
6.
Draw the free body diagrams for the underlined bodies in the following examples. State reaction forces for every
force.
a) Evan hangs from a rope attached to a ball, which is attached to the ceiling, by another rope.
b) Harshith slides along the ground and runs into Ahmed.
7.
Clifford (60 kg) and Pat (90 kg) go skating on the canal. While both are gliding Pat pushes Clifford with a force of
60 N [E]. What acceleration if any which each skater experience? (Please give a numerical answer(s) but no work
need be shown) [C - 1.000m/s2 [E], P – 0.6666m/s2 [W]]
8.
The following questions do not need work shown. Work shown will be checked for part marks in the case of an
incorrect answer.
a) A net force of 45 N [S] accelerates an object 6 m/s2 [S]. What is the object’s mass? [7.500 kg]
b) i) What is the force of attraction between Earth and the Moon? [1.981 x 1020 N]
ii) If the force of attraction between Mr. Moors (100 kg) and Earth is 245 N then how far is Mr.
Moors from the center of Earth? [1.276 x 107m] How far is Mr. Moors from the surface of Earth?
[6.38 x 106m]
c) What is the gravitational field strength on the surface of i) Mars [3.611 N/kg] ii) one radius of Mars above the
surface of Mars [9.029x10-1 N/kg] iii) on the surface of the Moon [1.617 N/kg] iv) two radii of the Moon above
the surface of the Moon? [1.797 x 10-1 N/kg]
d) A rope pulls Sydney (55 kg) upwards with an acceleration of 2 m/s 2. What is the force of tension in the rope?
(Sydney is off the ground holding onto to the rope for the whole question) [6.496 x 10 2 N]
e) An object experiences a certain force and acceleration. The object has its net force tripled and its mass cut in
half. What happens to the object’s acceleration? [Acceleration increases by 6x]
f) Two objects experience a gravitational force. The mass of both objects is cut in half while the distance between
them is tripled. What happens to the force between the two objects? [Force decreases by 36x]
9.
What causes friction on a molecular level? Give an example of how friction is a nuisance and give an example of
a benefit of friction.
10.
No work need be shown for the next calculations.
a) What is the gravitational force on a 53 kg girl? [5.199 x 102 N down]
b) What is the normal force on a 112 kg man standing on level ground? [1.099 x 10 3 N up]
c) What is the maximum static friction a 83 kg man experiences when the coefficient of static friction between his
shoes and the ground is 0.34? [2.768 x 102 N]
d) What is the coefficient of kinetic friction experienced by a 71 kg woman sliding with a constant velocity while
being pushed with an applied force of 156 N? [0.2240]
e) A man pulls with a force of 220 N on a rope connected to a 20 kg box which is connected by a rope to a 42 kg
box. The ground is frictionless. What is the acceleration of each box? What is the tension in each rope?
f) Repeat question e but with friction present (k = 0.11) [3.548 m/s2, 149.0 N between boxes, 220N in rope
connected to 20kg box] [2.469 m/s2, 163.2 N between boxes, 234.2 N in rope connected to 20kg box]
11.
A student (58 kg) stands on a scale in an elevator. What does the scale read in the following situations?
a) moving with a constant velocity of 4 m/s [up] [569.0 N] b) accelerating at 3.5 m/s 2 [up] [772.0 N] c)
accelerating at 8.2 m/s2 [down] [93.38 N] d) The student goes on a diet and rides the elevator and notices the
scale reads 450 N while the elevator is accelerating 1 m/s 2 [up]. How much mass did the student lose on the diet?
[16.37 kg]
12.
A 60kg student jumps off a 5 m rooftop onto the soft ground below. 0.15 s elapses as he comes to a stop once he
is in contact with the ground. (show complete solution)
a) What velocity did he hit the ground with? [9.905 m/s down]
b) What was the normal force exerted by the ground? [4551 N up]
13.
Karan (78 kg) is running at 8.9 m/s [W] when he jumps onto a new surface. It takes him 14 m to come to a sliding
stop? (show complete solutions)
a) What is the coefficient of kinetic friction of this new surface? [0.2884]
b) If Karan was pushed on this new surface with a constant force of 450 N for 3 seconds then what would his
velocity be at the end of these 3 seconds (assume he started from rest)? [8.820 m/s]
14.
A wood box (5kg) is pushed along the floor for 4 seconds. The initial velocity of the box is 1.75 m/s [L]. The
coefficient of kinetic friction for the surface and the box is 0.156. During the push the box accelerates at 1.25 m/s 2
[L].
a) What is the applied force? [13.90 N]
b) What is the displacement of the box during these four seconds? [17.00m]
15.
Mr. Moloughney pulls a couple of sleds (15 kg and 9 kg) connected in a line with a force of 150 N. What is the
acceleration of the system and what is the tension in the rope between the sleds (assume frictionless)? What is
the acceleration of the system and what is the tension in the rope between the sleds if the heavy sled has a
coefficient of friction of 0.08 while the light sled’s is 0.12 (the heavier sled is made of a more slippery material)?
(6.25 m/s2, 56.25 N), (5.318 m/s2, 58.46 N)
16.
A 15 kg object rests on top of a 10 kg object which rests on top of a 5 kg object which rests on the ground. What
force does each object push upwards with (normal force) and what is the normal force of the ground? (147.15 N,
245.25 N, 294.3 N)
Useful Information
v v
a 2 1
t
F  ma
d  (
F f   FN
v2  v1
at 2
at 2
d  v1 t 
d  v 2 t 
)t
2
2
2
Gm1m2
FR  F1  F2  F3 .....
FG 
r2
g = 9.81 m/s2 [down]
G = 6.67 x 10-11 Nm2/kg2
mearth = 5.98 x 1024 kg
mmars = 6.37 x 1023 kg
mmoon = 7.34 x 1022 kg
rearth = 6.38 x 106 m
rmars = 3.43 x 106 m
rmoon = 1.74 x 106 kg
rorbit of moon = 3.844 x108 m
v 2  v1  2ad
2
2