Name(s) _______________________________________________________________________ Hr. __
Physics, Practice Problems, Set 2, Unit 8b, Pushing and Pulling at angles
Problem 1: Pushing at a angle downward
The guy pushes a 20 kg lawn mower along the handle.
The handle makes a 50 degree angle with the horizontal
surface. The teenager pushes with a force of 55 N down
the handle as a pushing force. The man starts the lawn
mower from rest and gets it up to a horizontal speed of
2.0 m/s, in 5 sec. with a constant horizontal acceleration.
First off let's draw a force diagram...
a) What is the weight of the lawn mower? (196 N)
b) Use your two speeds and the time to determine the acceleration of the lawn mower. (0.4
m/s/s)
c) Come up with a horizontal force equation.
d) Use this equation to determine the frictional force. (27.35 N)
e) Come up with a vertical force equation.
f) Use your force equation to determine your normal force. (238 N)
g) Why doesn't your normal force = weight?
h) How far did the lawn travel during this acceleration (in meters)? (5 m)
i) Once the lawn mower reaches 2 m/s, you maintain this speed and stop accelerating the mower.
How hard do you have to push the mower now if you don't change the angle and the frictional
force doesn’t change? (42.5 N, notice the force gets smaller)
Pushing and Pulling at angles, practice problems, p. 1, Physics, Gleue
(2) Pulling a wagon
Ryan pulls his sister in a wagon. The wagon and his sister have a mass of 30 kg total. Ryan pulls
the wagon with a force of 50 N at an angle that is 30 degrees relative to the horizontal. There is
10 N of friction that acts horizontally due to the interaction of the wheels and the sidewalk
surface. Draw and label your force diagram.
10 N of friction
a) What is the applied force in the x direction (in Newtons)? (43.3 N)
b) What is the applied force in the y direction (in Newtons)? (25 N)
c) What is the weight of the wagon/sister? (294 N)
d) Come up with a force equation in the horizontal (x) direction.
e) Is the wagon accelerating or moving at a constant speed? How do you know?
f) If the wagon is accelerating determine the value of this acceleration. (1.11 m/s/s)
g) Come up with a force equation in the vertical (y) direction.
h) Calculate the force the ground exerts upward on the wagon's wheels (the normal force) (269
N)
i) Given the acceleration found above, how much time would it take to go 30 meters, if the
wagon starts from rest? (7.35 sec)
j) So how fast would the wagon be travelling at the end of this time given the above
acceleration? (8.16 m/s)
k) Would the above speed be realistic? (Nah, it's almost 20 mph; that would be going pretty fast
in a wagon!)
Pushing and Pulling at angles, practice problems, p. 2, Physics, Gleue
(3) Pushing and Pulling:
John and Jeremy are pushing AND pulling their brother, Jason, on the sled. John is pushing with
a force of 8 N at an angle of 60 degrees. Jeremy is pulling with an force of X Newtons at an
angle of 40 degrees. The sled and Jason have a mass of 20 kg. The snow provides a small
amount of friction, let's say 10 N. Let's also say that the sled is moving with a constant speed!
Make sure to always show a force diagram...
(a) Determine the horizontal and vertical parts of John's force.(4 N in the x direction and 6.93 N
in the -y direction or downward direction).
(b) Come up with a force equation in the horizontal (x) direction.
(c) Determine how hard Jeremy is pulling the sled. (7.83 N)
(d) What is the weight of sled/Jason? (196 N)
(e) Come up with a force equation in the vertical (y) direction.
(f) Determine the force that ground pushes upward against the blades of the sled (normal force).
(around 198 N depending upon rounding).
Pushing and Pulling at angles, practice problems, p. 3, Physics, Gleue
(4) Pushing a broom
The woman pushes the broom at a constant speed along
the floor. Her force is 15 Newtons along the handle. The
handle is angled at 50 degrees measured from the
horizontal. Determine the frictional force between the
broom and the floor. (9.64 N)
---------------------------------------------------------------------------(5) Pulling back on a vacuum
Let’s say the young woman pulls back on the vacuum with a force of 75 Newtons and let’s say
the angle between the handle of the vacuum and the horizontal is 50 degrees. The vacuum has a
mass of 15 kg. Determine the upward support from the floor (also called the Normal force).
(around 85.56 Newtons)
Pushing and Pulling at angles, practice problems, p. 4, Physics, Gleue