Download Physics – More Net Force Practice Problems

Physics Notes – Net Force Practice Problems
1) A 270,000 kg rocket in gravity-free space expels 270 kg of fuel by exerting a force of 360 N
on it. Find the magnitude of the acceleration of:
a) the fuel
b) the rocket
For numbers 2-7, draw a free-body diagram of each object that includes ALL the forces that act
on the object, and then find the magnitude and direction of the acceleration.
2) A 20.0 kg box is pulled to the left
with a force of 10.0 N across a
frictionless surface.
20.0 kg
3) A 14.5 kg box is pulled to the right
with a force of 40.0 N across a rough
surface, which applies a friction force
of 11.0 N acting on the box.
14.5 kg
kg
4) A 2.70 kg box is pulled to the left
with a force of 12.0 N. It moves at a
constant velocity of 2.00 m/s to the
left.
2.70 kg
kg
5) A 15 kg box sits still on a rough
inclined plane (no math required here).
6) A 60.0 kg student is in free-fall
(neglect air resistance).
7) A 60.0 kg student is falling at
terminal velocity (when the object has
been falling for so long, in the real
world, that the force of air resistance
matches the weight in magnitude).
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8) A 100.0 kg sign is suspended from a pole by two vertical strings which are equidistant from
the sign’s center. Find the magnitude of the tension in each string.
T1
T2
EAT AT
JOE’S
9) A second sign (mass = 25.0 kg) is suspended from the first by a single string. Find the
magnitude of the tension in each of the three strings now.
T1
T2
EAT AT
JOE’S
T3
Good
food
For problems 10 – 12, draw the free-body diagram for each object, find the magnitude of each
object’s acceleration (magnitude only). Assume all surfaces are frictionless.
10)
25.0 kg
F = 50.0 N
11)
attached by a massless string
F = 50.0 N
20.0 kg
5.00 kg
12)
massless string
frictionless, massless pulley
20.0 kg
5.00 kg
13) For each of these, the picture shown is a top-down view of the object so
that weight and normal force are not considered. For each, determine the
magnitude and direction of the net force acting on the object. Refer to the
compass rose at the right.
a)
b)
c)
F1 = 5.00 N
F1 = 3.0 N
F2 = 4.0 N
5.0
kg
5.0
kg
F1 = 25.0 N
5.0
kg
F2 = 25.0 N
F2 = 10.0 N
14) A 6.00 kg box is pulled to the left across a frictionless surface by a force of 20.0 N directed
at 45o above the horizontal. The box does not move vertically.
20.0 N
45.0o
6.00 kg
a) Resolve the 20.0 N vector into its horizontal and vertical components, using the
trigonometric functions.
b) Determine the magnitude of the normal force (will it be equal to the weight?).
c) Determine the magnitude and direction of the acceleration.