Download Solving Impulse and Momentum Problems and more Lecture notes Physics in PDF only on Docsity!
Textbook: Physics for Scientists and Engineers 3 Edition by Randall Knight
STEM Success Center
Physic 201
Phys 201: Chapter 9 Impulse and Momentum
Before we begin the problems, it helps to list your knownโs and unknowns/what we are solving for. This
helps with organization by identifying the what the problem is asking for. Also, red represents the
solution.
Section 9.2: Solving Impulse and Momentum Problems
12) A 250 g ball collides with a wall. The figure below shows the ballโs velocity and the force exerted on
the ball by the wall. What is ๐ฃ
๐๐ฅ
, the ballโs rebound velocity?
Known:
๐
๐๐
๐ฅ
Find:
๐๐ฅ
Given that a force is being applied to an object during a time interval, then find the impulse ( ๐ฑ ๐
๐ฅ
๐ฅ
8 ๐๐
0 ๐
[
๐
๐
]
๐ก
๐
๐ก
๐
= 500 [ 0. 008 ๐๐ โ 0 ๐ ] = 4 ๐ โ ๐
Now, use the impulse-momentum theorem (โ๐ ๐ฅ
๐ฅ
) to solve for the final velocity.
๐ฅ
๐ฅ
๐๐ฅ
๐๐ฅ
๐ฅ
๐
๐๐ฅ
๐
๐๐ฅ
๐ฅ
Textbook: Physics for Scientists and Engineers 3 Edition by Randall Knight
STEM Success Center
Physic 201
๐
๐๐ฅ
๐ฅ
๐
๐๐ฅ
๐๐ฅ
๐ฅ
๐
๐๐ฅ
๐๐ฅ
Section 9.3: Conservation of Momentum
16) A 10-m-long glider with a mass of 680 kg (including the passengers) is gliding horizontally through the
air at 30 m/s when a 60 kg skydiver drops out by releasing his grip on the glider. What is the gliderโs
velocity just after the skydiver lets go?
Known:
๐
= 60 ๐๐ (mass of skydiver)
๐บ+๐
= 680 ๐๐ (mass of glider plus the mass of skydiver)
๐บ
๐บ+๐
๐
= 680 ๐๐ โ 60 ๐๐ = 620 ๐๐ (mass of glider)
๐บ
๐
๐
Note: turns out as the skydiver releases, the skydiverโs final velocity will be the same as gliderโs initial
velocity thus,
๐
๐
๐บ
๐
Find:
๐บ ๐
Using the Law of Conservation of Momentum equation (๐ท
๐
๐
๐บ
๐บ
๐
๐
๐
๐
๐บ+๐
๐บ
๐
Substitute ๐ฃ
๐บ
๐
for ๐ฃ
๐
๐
given that ๐ฃ
๐
๐
๐บ
๐
, then solve for the gliders final velocity
๐บ
๐บ
๐
๐
๐บ
๐
๐บ+๐
๐บ
๐
Textbook: Physics for Scientists and Engineers 3 Edition by Randall Knight
STEM Success Center
Physic 201
To check your answer, see if the momentum of the clay is same as the momentum of the car.
Section 9.6: Momentum in Two Dimensions
25) A 20 g ball of clay traveling east at 3.0 m/s collides with a 30 g ball of clay traveling north at 2.0 m/s.
What are the speed and the direction of the resulting 50 g ball of clay?
Known:
1
๐๐ฅ
1
2
๐๐ฆ
2
Find:
๐
Use the Law of Conservation of Momentum (๐ท ๐
๐
) to solve for the clayโs velocity
๐
๐
Textbook: Physics for Scientists and Engineers 3 Edition by Randall Knight
STEM Success Center
Physic 201
X-direction: ๐
1
๐๐ฅ
1
2
๐๐ฅ
2
1
2
๐๐ฅ
Rewrite ๐ฃ
๐๐ฅ
in terms of ๐ฃ
๐
using trigonometry.
cos(๐) =
๐๐ฅ
๐
๐๐ฅ
๐
cos(๐)
1
๐๐ฅ
1
2
๐๐ฅ
2
1
2
๐
cos(๐)
๐
cos(๐) =
1
๐๐ฅ
1
2
๐๐ฅ
2
1
2
๐
cos(๐) = 1. 2
Y-direction: ๐
1
๐๐ฆ
1
2
๐๐ฆ
2
1
2
๐๐ฆ
Rewrite ๐ฃ
๐๐ฆ
in terms of ๐ฃ
๐
using trigonometry.
sin
๐๐ฆ
๐
๐๐ฆ
๐
sin
1
๐๐ฆ
1
2
๐๐ฆ
2
1
2
๐
sin(๐)
๐
sin(๐) =
1
๐๐ฆ
1
2
๐๐ฆ
2
1
2
๐
sin(๐) = 1. 2
Use the Pythagorean theorem ( ๐
๐
๐
๐
) to find ๐ฃ
๐
, thus
๐
2
๐๐ฅ
2
๐๐ฆ
2
Substitute ๐ฃ
๐๐ฅ
and ๐ฃ
๐๐ฆ
(which was found above):
๐
๐๐ฆ
๐๐ฅ
