Momentum, elastic energy and Impulse Flashcards
What is momentum?
Momentum is known as the measurement of mass in motion.
Think of it as:
how much mass is in how much motion
What is the formula for momentum?
P = mv
Momentum = Mass x Velocity
Where ‘p’ is momentum (Kg ms-1)
‘m’ is the mass of the object (Kg)
v is the velocity of the object (ms-1)
Is momentum a vector quantity?
Yes, momentum is a vector quantity since there is direction involved
What is elastic energy? When a collision is considered perfectly elastic, what does it mean?
In elastic collisions, the total kinetic energy before a collision and after it is equal to each other. This is due to the Law of Conservation of Kinetic Energy. Therefore, an elastic collision is where BOTH KINETIC ENERGY AND MOMENTUM IS CONSERVED BEFORE AND AFTER THE COLLISION. (MUST MENTION BOTH MOMENTUM AND KINETIC ENERGY)
When a collision is considered ‘inelastic,’ kinetic energy is converted into other types of energy such as thermal and sound energy. THEREFORE, AN INELASTIC COLLISION IS WHERE KINETIC ENERGY IS NOT CONSERVED BUT MOMENTUM IS. MUST INCLUDE MOMENTUM IN THIS.
When do we use mechanical energy to find out certain values in an energy question?
Mechanical energy only deals with energy resulting from position and motion. In short, it is where only kinetic energy and gravitational potential energy are considered.
Therefore, the initial mechanical energy is equal to the total mechanical energy after its change in motion or position.
E (initial) = E (Final)
1/2mu^2 (initial velocity) + mgh (initial height)
= 1/2mv^2 (final velocity) + mgh (final height)
When a force is exerted on an object which doesn’t move, such as a wall, is work done on that object?
No, since there is no displacement involved despite the force applied. Therefore, no work is done on this object
When an object is carried at contact velocity by a force, is work done to this object? An example includes carrying a box around.
No, work is not done on this object.
Due to constant velocity, that means the net force is zero since the acceleration is zero. If the net force is 0, then either there is no force applied or the forces are balanced, meaning that the box is technically not moving in an imbalanced manner. As a result, no work is done to it due to no extra change in force or displacement.
If the question asked
How much work is done for an object continue with its constant motion or acceleration if there is a friction force of …?
(given how much they travelled)
Then what do you do?
The force required for the car to continue with its motion will be compromised due to friction force. Therefore, the force needed is the force required to overcome the friction force.
Therefore, work = force x displacement. But here,
Work = Friction Force x displacement
If the net force is zero due to constant velocity, then does that mean that the object has entirely no forces acting on it at all?
Yes or no
No, if the net force on an object is zero, it means that the vector sum of all the forces acting on the object is zero. This does not necessarily mean that there are no forces acting on the object at all, but rather that the forces acting on the object are balanced in such a way that there is no resulting motion or acceleration.
Therefore, no. There are still forces applied to this object in a way that they are balanced and cancel out each other to sumass to zero
If an object is travelling in a circular motion such as in a roundabout, at a constant velocity of 5ms^1, is the net force of this object zero?
No, the net force will NOT BE ZERO
This is because although the magnitude of the velocity is constant and the same throughout, it is still changing its velocity due to the change in DIRECTION.
We must also account for the change in direction, which is why the net force is NOT zero.
Constant velocity doesn’t always mean 0 net force if the direction of the object is always changing as that technically means that the velocity is still changing.
Extra) If it said constant speed, then we are unable to calculate the net force, since force only deals with vector quantities such as acceleration. Speed does not give a direction so we cannot use this value.
If given a large number such as 109,119 how would you round this off to two sig figs?
Use scientific notation
Therefore, 1.1 x 10^5 joules
