# Physics - Recall for Chapter 7: Laws of Motion and Momentum

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-7-laws-of-motion-and-momentum/ · Updated: 2021-08-03 · Tags: physics, school, laws-of-motion-and-momentum, recall-questions

## Recall Questions
##### State Newton's first law??
The velocity of an object will only change if a resultant force acts on it.

##### State the ways in which an object's velocity might change??
An objet may accelerate, decelerate, or change direction.

##### State Newton's third law (long)??
When two objects interact, they exert forces on each other that are equal in magnitude, opposite in direction and of the same type.

##### State the four features of a Newton's third law pair of forces??
1. Equal magnitude.
2. Opposite directions.
3. Same type.
4. On different objects.

##### State and explain whether momentum is a scalar or vector quantity??
Vector, as momentum is the product of mass and velocity, and velocity is a vector.

##### State the SI unit of momentum??
$$kgms^{-1}$$

##### State the principle of conservation of momentum (long)??
In a closed system, where no external forces act, the total initial momentum is equal to the total final momentum.

##### What is an elastic collision??
A collision in which kinetic energy and momentum are both conserved.

##### What is an inelastic collision??
A collision in which kinetic energy is not conserved, but momentum and total energy are still conserved.

##### State Newton's second law??
The resultant force acting on an object is equal to the rate of change of momentum of the object.

##### State the special form of Newton's second law used when mass is constant??
$$F = ma$$

##### Define the impulse of a force??
The product of the magnitutde of the force and the time it acts for.

##### What is the equation for the impulse of a force??
$$\text{Impulse} = Ft$$

##### What does impulse represent??
The change in momentum.

##### What does the area under a force-time graph represent??
Impulse/change in momentum.

##### How can the conservation of momentum be applied to collusions in two dimensions??
Momentum in the $x$ and $y$ directions are conserved seperately.

##### What happens to objects that collide perfectly inelastically??
They stick together.

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