Chapter 8: Linear Momentum and Collisions Flashcards
Define change in momentum
the difference between the final and initial momentum; the mass times the change in velocity
Define conservation of momentum principle
when the net external force is zero, the total momentum of the system is conserved or constant
Define elastic collisions
a collision that also conserves internal kinetic energy
Define impulse
the average net external force times the time it acts; equal to the change in momentum
Define inelastic collision
a collision in which internal kinetic energy is not conserved
Define internal kinetic energy
the sum of the kinetic energies of the objects in a system
Define isolated system
a system in which the net external force is zero
Define linear momentum
the product of mass and velocity
Define perfectly inelastic collision.
a collision in which the colliding objects stick together
Define point masses:
structureless particles with no rotation or spin
Define quark
fundamental constituent of matter and an elementary particle
Define second law of motion
physical law that states that the net external force equals the change in momentum of a system divided by the time over which it changes
What is the equation for linear momentum
p=mv
p=momentum
m=mass
v=velocity
What is the unit for momentum?
kgm/s
What is Newton’s second law in symbols?
Fnet = ΔpΔt
What is the equation for impulse?
Δp = fnet Δt
How to calculate acceleration
a = ΔV / ΔT
ΔV = V-Vo
What are the two type of collisions?
Elastic and inelastic
What is elastic collions?
Where kinetic energy is conserved
What is inelastic collision?
Kinetic energy is lost in the collision.
Elastic collisions mostly occur…
In microscopic particles
How to calculate the veloctiy of the center of mass?
Vcom = (m1v1+m2v2)/m1+m2
A person slaps her leg with her hand, which results in her hand coming to rest in a time interval of 2.65 ms from an initial speed of 3.25m/s. What is the magnitude of the average contact force exerted on the leg, assuming the total mass of the hand and the forearm to be 1.65kg?
2023.6 N
Explanation:
I. Assess what you have: time interval, initial speed, and mass
II. Assess what you need: average force
III: Find a fitting equation: Δ𝑝=𝐹Δ𝑡
a. Rearrange equation –> F = Δ𝑝/Δ𝑡
b. substitute with what we have –> F = m(vf-vi)/Δ𝑡
c. Since final velocity is 0 we get our final equation…
d. F = -mvi / Δ𝑡
IV. Plug in numbers: F = -(1.65kg)(3.25m/s) / 2.65x10^-3
V. Solve: 2023.6
Calculate the momentum Pelephant of a 2060kg elephant charging a hunter at a speed of 7.51m/s
p = mv
p = 2060 kg * 7.51m/s
p = 15,470.6 kgm/s
What is the momentum Phunter of the 87.0kg hunter running at 7.39m/s after missing the elephant?
642.93kgm/s
p = mv
p = 87 * 7.39
p = 642.93
A large semitailer truck and a small car have equal momentum. How do their speeds compare?
The truck has a much slower speed than the car.
Explanation:
If the masses are only slightly different, then the speeds will be only slightly different. In this case, there is a large semitrailer truck and a small car.
A rubber ball and a wet lump of clay, both with mass 6kg, are thrown at a wall with the same speed, 6m/s. The ball bounces off the wall with no loss of speed, but the clay sticks.
What is the change in momentum of the clay and the ball, respectively?
Ball: -36 kgm/s
Clay: -72kgm/s
The inital momentum of them is the same. p=mv –> p = 6kg * 6m/s = 36kgm/s
Since the ball bounces off but keeps going it is just the opposite direction, -36kgm/s. But since the clay stops it doubles to -72kgm/s
