A
What is a Force?
A push or a pull exerted on a body
If a car accelerates, is the system of horizontal forces acting on it either balanced or unbalanced?
Unbalanced
State 2nd Newton's law
Net/Resulting Force = mass * acceleration
What is momentum (concept and formula)
The ability to move objects (p=m*v)
What is impulse
Impulse is the change in momentum of a system (one or more objects).
Is Force a vector or a scalar quantity?
A vector quantity (it has magnitude and direction)
What is inertia?
The resistance to the change in the status motion.
Why does an airplane manage to fly while a wal doesn't (even though they are both subjected to 3rd Newton's law)?
Because on a wall action and reaction are applied on the same object (the wall) while on an airplane the action is applied on the gas and the reaction is applied on the airplane.
What is an isolated system?
A system of (one or more) objects where no external forces are acting, affecting the system.
Example of external forces:
- Friction (includinh air resistance)
- Force of gravity
Is impulse either a vector or a scalar quantity?
A vector quantity
Name the instrument to measure Force
Dynamometer
True or False?: The acceleration of an object always points to the same direction as the "net/resulting" Force on that object.
True
Is the acceleration of a car zero or non-zero when no net force acts on it? Explain your answer.
a=0 m/s/^2. The car is either at rest or at constant velocity.
Is the resulting momentum of 2 colliding (or separating) objects conserved in a non-isolated system?
No, the resulting momentum is not conserved because external forces affect the eventual motion within the system of the 2 objects.
There are 2 formulas of impulse, one is final momentum - initial momentum, and the other is...
Impulse = Average Force * time
A flying airplane is affected by 4 forces: the weight (or force of gravity), the air resistance, the thrust, and the ...
Upthrust (or lift)
True or False: If the "applied force" on an object points to the right, the object always accelerates to the right.
False
A car of mass 1200 kg is acted upon by a net force of 300 N in the direction of its motion. If its initial velocity is 3 m/s and the force acts for 15 s, calculate its final velocity.
Final velocity = 6.75 m/s (along the direction of motion)
A sticky ball of mass 0.2 kg is thrown horizontally towards a stationary cart of mass 2 kg. The ball hits the cart and sticks to it. Immediately after the collision, the cart and ball move together at 3 m/s.
Assuming the ball–cart system is isolated, calculate the velocity of the ball immediately before the collision.
ball's velocity = 33 m/s in the direction of the cart's motion.
A ball of mass 0.3 kg travels horizontally towards a wall at 5 m/s, moving to the left. It hits the wall and rebounds horizontally to the right at 4 m/s.
Calculate the impulse acting on the ball during the collision.
Impulse = 2.1 (kg*m/s), to the right
If a car moves at constant velocity, is the system of horizontal forces acting on it either balanced or unbalanced?
balanced
True or False: The lower the mass of an object the higher its inertia.
False
A car is travelling at 20 m/s when a net force of magnitude 4000 N acts on it, causing it to "decelerate" uniformly until it stops after 5 s.
Calculate the mass of the car.
m = 1000 kg
A rocket of total mass 1500 kg travels horizontally at 60 m/s. It releases 120 kg of gas backward, and the gas moves at 90 m/s.
Assuming no external horizontal forces act on the rocket–gas system, calculate the rocket's velocity immediately after the gas is released.
Rocket velocity = 73 m/s opposite to the direction of the released-gas velocity.
A tennis ball of mass 0.2 kg is moving at 15 m/s towards a wall. It rebounds in the opposite direction at 10 m/s. The average force exerted by the wall on the ball is 500 N.
Calculate the time for which the force acts on the ball.
t=0.01 s (time of the impulse)