Module 3 Newton's Law Of Motion Flashcards
State Newton’s second law of motion.
The resultant force is proportional to the rate of change of momentum and the direction of the change of momentum is in the direction of the force.
What are the differences between Newton’s first law and third law?
The first law only considers the forces acting on the same body and the forces are of different types.
Whereas for the third law, the forces are of the same type and act opposite to each other on different objects.
Explain how the momentum of a gun equals zero after it has been shot from rest.
At rest the velocity of gun and bullet is zero, this means zero momentum as p=mv.
Since momentum is always conserved the momentum afterwards must equal zero. This can be justified as one of the bodies( gun or bullet) will have a positive velocity and the other will have a negative velocity. The sum of both their momentums after shooting would then equal zero, conserving momentum.
Is momentum a scalar?
No, it’s a vector.
State the principle of conservation of momentum.
The principle states that the total momentum before a collision equals the total momentum afterwards, considering no external forces are acting on the bodies.
What is impulse? Sate SI units.
Impulse is the product of the force acting on a body and the duration it acts upon in seconds.
The SI units are Ns.(kgm/s)
Show how impulse is equal to change in momentum.
F=ma a=v-u/t F=m x (v-u/t) F=mv - mu/t Ft=mv - mu
Explain how seatbelts reduce the forces acting on passengers in crash?
Seatbelts increase the time taken for impact or momentum to change. This decreases the forces acting on passengers as by F=mv-mu/t, F is inversely proportional to t. This reduces the acceleration of passengers towards the dash.
What is area under Force time graph?
Area is equal to the impulse of a force.
How do you calculate momentum in two dimensions?
As momentum is always conserved in all directions.
First equate and solve all the given values in the x direction then the y.
Finally find the resultant of these 2 values using Pythogeras theorem to find the final value. You can also use tan to find the angle of the force from the horizontal.
Define perfectly elastic and in-elastic collisions.
Collisions where all momentum and kinetic energy is conserved before and after collisions are perfectly elastic.
In inelastic collisions momentum is conserved but some kinetic energy is lost to surroundings in other forms.
When a racket hits a ball, what is the main reason why any calculated values for speed, mass or momentum will be higher than actual?
The momentum of the person holding the racket also changes.
While applying Newton’s third law to bodies, what 2 things should you talk about?
How the forces acting are equal and opposite
And
How the time of contact is always the same for both.
What happens to acceleration if the gradient turns from positive to negative, but stays above the x axis, on a force time graph?
As gradient is originally positive, acceleration is increasimg.
When gradient turns negative acceleration will decrease but will still be positive, until the graph goes below the x axis
