Lab Skills & Concepts
What data do we need to determine the momentum of a cart and what lab equipment can we use for these measurements?
1. The mass of the cart with a mass scale
2. The velocity of the cart with a motion tracker (or meterstick + stopwatch)
What is recoil?
An interaction in which two objects push each other apart. The objects have the same initial velocity and momentum is conserved.
What is the equation for momentum?
p=mv
What must be true about the forces between two carts during a collision?
The magnitude of the forces must be the same by Newton's 3rd Law and for momentum to be conserved.
List two features a correct lab procedure should include.
A lab procedure should include:
- Written as an ordered list of steps
- Describes each measurement
- States what equipment is used for each measurement
- States which steps are repeated, how many trials are conducted, and what is changed in each trial
- Does not describe or include calculations
What is the difference between a totally inelastic and an elastic collision?
In an elastic collision, two objects collide and bounce apart. Energy is conserved,
In a totally inelastic collision, two objects collide and stick together. Energy is not conserved.
What equation do we apply to determine the final velocity of an object after a collision (or recoil)?
The collision equation:
p_1+p_2=p_1'+p_2'
What is the relationship between force and time for a given impulse?
Force and time are inversely proportional: the greater the applied force, the less time it will take to change the momentum of the object.
A student is testing the following scientific question: "What is the effect of the initial velocity of a cart on its final velocity after colliding with another cart?"
What is the dependent variable in the scientific question?
The final velocity after the collision - the student will measure the effect of the independent variable on this variable.
Momentum is normally conserved in a closed system. When will momentum not be conserved?
When there are external forces or objects acting on parts of our system (such as friction, or another object colliding with part of our system).
What are the two ways of calculating impulse?
J=Deltap=p_f-p_0
&
J=FDeltat
A 2 kg cart travelling at +5 m/s collides with a 1 kg cart travelling at +1 m/s. The two carts stick together and travel at the same velocity.
The final velocity of the two carts is closer to the initial velocity of which cart? Justify your answer.
(hint: which one has a smaller change in velocity?)
The final velocity must be closer to the initial velocity of the 2 kg cart. It will have a smaller change in velocity (because it has a greater mass), so the final velocity will be between 3 and 5 m/s.