Dynamics Review Practice
1. What is the strength of the gravitational field (in
N/kg) at an orbit of 1.0 x106 m above the planet Zoklopgniald with
mass of 3.45 x1026 kg and mean radius of 7.80 x107m? 3.69 N/kg What is the gravitational force
exerted on a 2840 kg satellite orbiting Zoklopgniald at this altitude? 10 500 N
2. What is the force of gravity between two electrons
(mass = 9.11 x 10-31 kg) that are 1.0 m apart? 5.54 x 10-71 N
3. What is the strength of the gravitational field 10.0
metres away from your body? About 5.0 x 10-11
N/kg
1. A sled is being pulled to the right with a force of 28
N. A frictional force is working opposite the applied force with a magnitude of
17 N. The mass of the sled is 4.5 kg. (a) What is the net force in the x
direction? 28 Ð 17 = 11 N (b) What is the
coefficient of friction between the sledÕs blades and the surface? m = 0.385
2. A football player with a mass of 86 kg, dives into the
end zone and is slowed by the grass after he hits the ground by a force of
friction of 580 N. What is µ
between the player and the grass? m = 0.69
3. A person pushes horizontally with a force of 350 N on
a 68 kg chair to move it across a level floor. The coefficient of friction is
0.37. (a) What is the magnitude of the frictional force? 247 N (b) What is the acceleration of the
chair? Fnet = 350 Ð 247 = 103 N,
acceleration = 1.51 m/s2
1. A spring mechanism at the end of a cart has a k = 480
N/cm. The cart, on the spring side, is held up against the wall, causing a
distortion on the spring of 3.8 cm. (a) Calculate the restoring force of the
spring. 1824 N (b) If the cart has a
mass of 1.050 kg, what will its acceleration be on the frictionless surface? Felastic=Fnet therefore 1737 m/s2
2. A certain spring, hanging vertically, is distorted by
42.0 cm when it has a 350 g mass placed on it. Felastic=Fg
therefore F = kx = 8.17x where k=8.17 N/m What
will the distortion be if (a) the mass is replaced by a 250 g mass 30.0 cm or 0.300 m, and (b) a 1.00 kg mass 1.20 m or
120.0 cm?
NewtonÕs Laws & Free
Body Diagrams
1. An unbalanced force of 72 N acts on a 8.0 kg object.
If the object was initially at rest what will be its velocity after 4.0 s? acceleration = 9.0 m/s2, use kinematics to
find vf = 36 m/s
2. A 4.0 kg object accelerates from rest traveling 24 m
in the first 4.0 s. What is the net force exerted on this object during
acceleration? acceleration = 3.0 m/s2
using kinematics d=vit + 1/2at2,
then use NewtonÕs 2nd Law to find that Fnet = 12 N
3. A 16 N force pushes on an object towards the east. A
14 N force pushes on the same object towards the west. (a) What is the net
force on the object? 2 N to the east (b)
If the object is observed to accelerate at 0.50 m/s2, what is the
objectÕs mass? 4.0 kg
4. A 24 kg mass is observed to accelerate from rest at
4.0 m/s2 towards the east. The applied force acting on the mass is
120 N. (a) What is the net force acting on the mass? Fnet
= 96 N (b) What is the force of friction acting on this mass? Fapplied - Fnet = Ffr =
24 N (c) If, when the speed of the object has reached 12 m/s the
applied force is removed, how long will it take the object to stop? The only force now acting on the mass is friction and so
Fnet = - Ffr, the mass decelerates at Ð1.0 m/s2
taking 12 s to stop (d) How far will the object have traveled before
it stops? Use kinematics to find that d = 72 m
5. A 22 kg sled is being pulled up a slope at a constant
speed of 3.0 m/s. What is the net force on the sled if the applied force is 17
N? Fnet is zero (moving at constant
velocity!!)
1. What is the momentum of a bird of mass 22 g traveling
at 11 m/s? p= 0.24 kg¥m/s
2. A child throws a rock of mass 5.40 kg horizontally
from a canoe with velocity of 10.0 m/s. This causes the canoe to slip backwards
as the rock flies forward. Calculate the resulting velocity of the canoe,
assuming it was initially at rest. The mass of the child is 25.0 kg and the
mass of the canoe is 55.0 kg. v = 0.68 m/s
3. An open railroad car of mass 11 000 kg travels alone
on a level frictionless track with a constant velocity of 18.0 m/s. A 6 500 kg
load is dropped onto the car. What will its new velocity be? v = 11.3 m/s
4. A golf ball of mass 0.0450 kg is hit off the tee at a
speed of 50.0 m/s. The golf club was in contact with the ball for 0.00500 s.
Find (a) the impulse on the golf ball 2.25 N¥s,
and (b) the force exerted on the ball by the club.
450 N