Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is...
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Transcript of Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is...
![Page 1: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/1.jpg)
Energy & Momentum Problems (CP)
Mixed
![Page 2: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/2.jpg)
Rule of Thumb: If the mass of the object stays the same it is
a conservation of Energy problem. If the mass of the object changes, it is a
conservation of momentum problem (inelastic collision)
If two objects bounce, it is a conservation of momentum problem (elastic collision)
If there is a spring, it is an energy problem
![Page 3: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/3.jpg)
Example: A block with a mass of 25 kg starts from rest 6.0 m above the ground and slides down a frictionless ramp. What is the velocity of the block at the bottom of the ramp?
21(25 )(9.8)(6.0 ) (25 )
2kg m kg v
21
2mgy mv
Ei = Ef
Mass stays the same
V = 10.84 m/s
Draw the picture:
![Page 4: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/4.jpg)
Example: At the bottom of the ramp, the 25 kg block collides inelasticly with 10. kg toy car at rest. What is the final velocity of the car-block combo?
pi = pf
Mass changes
(25 )(10.84 / ) 0 (25 10. ) fkg m s kg kg v
Vf =7.7 m/s
Draw the picture:
V=10.84 m/s
![Page 5: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/5.jpg)
Example: 2:a) A 65 kg Olympic ice skater is coasting at 5.0 m/s on a frozen pond when his little brother (of mass 35 kg) falls from a tree and lands in his arms. Now how fast is the skater moving while still holding his brother? (ignore any velocity from his little brother)
pip
f
(65kg)(5.0m / s)0(65kg35kg)vf
vf3.25m / s 3.3m / s
b) The sudden appearance of his brother makes the skater hit a small stone and fall over. The friction between his jeans and the ice bring him, still holding his brother, to a stop in 1.5 m. What is the force of friction between his jeans and the ice?
KEiW
f
1
2mv
i
2 Ffd
12(6535)(3.25)2 F
f1.5
NNFf 350352
![Page 6: Energy & Momentum Problems (CP) Mixed. Rule of Thumb: If the mass of the object stays the same it is a conservation of Energy problem. If the mass of.](https://reader036.fdocuments.net/reader036/viewer/2022083009/5697bfe11a28abf838cb404e/html5/thumbnails/6.jpg)
Example: 2
A 0.25 kg Nerf arrow is fired from spring-loaded gun at a 10.0 kg target sitting on a frozen (frictionless) pond. After impact, the arrow and target slide across the pond at 3.7 m/s. What is the spring constant of the Nerf gun if the spring was compressed 30.0 cm when the arrow was fired? (assume the arrow does not fall during flight) (Yes, I know this is a little unrealistic)
K = 64,000 N/m