🟢 Momentum Basics
A 3 kg object moves at 4 m/s. What is its momentum?
12 kg·m/s
Impulse equals what two quantities?
change in momentum OR area under an F–t graph
In a perfectly inelastic collision, what quantity is conserved?
momentum
A 3 kg block slows from 4 m/s to 2 m/s. What happened to its kinetic energy?
it decreased
Why does an airbag protect a driver?
it increases stopping time
Momentum is conserved in a system when what condition is met
when there is no net external force
If a force-time graph is triangular, how do you calculate impulse?
½ base × height
In an elastic collision, what two quantities are conserved?
momentum and kinetic energy
If speed decreases across a rough section, what force caused the change in momentum?
friction
Does an airbag reduce the driver’s momentum change?
no — it increases stopping time, not Δp
If a 4 kg object moving left sticks to a 3 kg object moving right, what additional information is needed to determine the final direction?
the initial speeds of the objects
If force is positive at first and negative later, what can happen to momentum?
it can increase, then decrease and possibly reverse direction
A brother twice as massive as his sister is pushed on frictionless ice. If the sister has KE = K, what is the brother’s KE?
What is K/2
Average force equals what two quantities divided?
change in momentum divided by time
If initial KE increases, why might more energy be lost in a non-elastic collision?
more deformation occurs at higher speeds
The center of mass speed of a two-cart system during a collision on a frictionless track does what?
it does not change
A block is pushed in the positive direction. The force decreases linearly to zero. What happens to momentum?
it increases by approximately ½F₀t
A 2 kg block slides down a frictionless incline and sticks to a 3 kg block. What principle MUST be used to find final speed?
conservation of momentum
Work done by friction equals what?
change in kinetic energy
How would you test whether KE loss depends on initial speed?
vary initial speed and measure fractional KE lost
A 1.0 kg cannon fires a ball. Why do we only use horizontal momentum conservation
because there is no external horizontal force, but vertical forces (normal + gravity) act
Which graph can determine rebound speed: Force vs Time or Force vs Position?
either graph can be used
If two carts stick together, the fraction of kinetic energy lost equals what expression?
m₂ / (m₁ + m₂)
If a block crosses a rough section in 0.5 s and momentum decreases by 6 kg·m/s, what is the average friction force?
12 N
How do you calculate fractional kinetic energy lost
(Kinitial − Kfinal) / Kinitial