PHYSICS FINAL EXAM CH. 2-8 Flashcards
(38 cards)
What is the difference between speed and velocity?
Speed is the rate of motion; it is a scalar. Velocity is directed speed; it is a vector
What are the three (3) different ways an object can accelerate?
Change (increase/decrease) speed; change direction; or change both speed and direction
Define instantaneous speed. What is a common instrument that measures this type of speed?
It is a speed at a specific time, typically measured using speedometers
Which shows an object that is - at rest? moving with constant
velocity? moving backwards? accelerating?
At rest; moving backwards; moving with constant velocity; accelerating
What are the units for force, weight, mass, and acceleration?
- Force is in Newtons or N. 1 N = 1 kg m/s2
- Weight is a force, so it is also in Newtons or N. It is also called gravitational force or force of gravity.
- Mass is in kilograms or kg.
- Acceleration is in m/s/s or m/s2
Explain each of Newton’s laws of motion
- First Law: A body at rest stays at rest, or a body in motion stays in motion with constant speed and
direction, unless acted upon by an unbalanced force. - Second Law: F = m a; the acceleration of an object is equal to the ratio of the net force over the mass.
- Third Law: For every action force, there is an equal but oppositely directed reaction force
Compare mass and weight
Mass is the amount of material. It is constant. Weight is the gravitational force between a mass and
another object (like the earth). It varies
Does mass ever change? If an object’s mass on earth is 1 kg, what is its mass on Jupiter?
Mass is constant. If m = 1 kg on earth, it will also be the same on Jupiter, or anywhere in the universe
A 10-N force and a 4-N force act on an object simultaneously. What is the largest (maximum) net force
that could act on the object? What is the smallest (minimum) net force that could act on the object?
- Largest when the two forces are in the same direction. – 14 N.
- Smallest when the two forces are in opposite directions. – 6 N
Forces always occur in _____
pairs; This is a consequence of Newton’s 3rd_ law of motion
If an object weighing 500 N is suspended motionless from a rope, how much force does the rope exert on
the object?
The force the rope exerts on the object is also 500 N.
You have a 10-kg object and a 20-kg object. Which has more inertia? If they are both moving at 5 m/s,
which would be harder to stop and why?
- The 20-kg object has more mass, and therefore more inertia.
- If both are moving with the same speed, the 20-kg object will have more momentum (inertia of
motion) and therefore would be harder to stop
Define friction. Name and describe the different types of friction
- Friction is a resistive force.
- Types: static (when object is at rest); kinetic (when object is moving)
Accelerations are caused by _____
unbalanced net forces
A book rests on a table. What forces act on it?
The object’s weight, and the table’s support (normal force).
When is an object in free fall?
When the only force acting on the object is gravity, it is in free fall
What is the value of the acceleration due to gravity? What is this commonly called?
9.8 m/s2 or rounded to 10 m/s2. It is also small g
If a ball is thrown straight up in the air, what happens to its speed and acceleration? What is the speed at
the top of its trajectory? What forces are acting on it at different points in its motion?
The speed decreases on its way up and gets to zero at the maximum height. The acceleration is constant
at all times, and is g. The only force acting on the object is gravity
When does a falling object reach terminal velocity?
Terminal velocity is reached when the air resistance equals the object’s weight
What does air resistance depend on?
Speed, frontal surface area
What is the momentum of a 1400-kg car parked on the side of the road?
Nothing. Momentum is mass times velocity. A parked car has zero velocity.
Why does the cannon not go back as quickly (recoils) as the cannon ball if the same amount of force acts
on both?
The same force acts on the cannon and the cannonball but their accelerations will not be the same. The
smaller mass (cannon ball) accelerates more (a = F/m) and therefore moves faster after the explosion.
The cannon which has a bigger mass accelerates less and therefore recoils at a smaller rate
If an object’s velocity doubles while its mass stays the same, what happens to its momentum? (stay the
same, doubles, quadruples) What if the mass doubles but the velocity stays the same?
Momentum is mass x velocity. Momentum is directly proportional to mass and velocity. If either the
mass or the velocity doubles and the other quantity stays the same, the momentum doubles
How would you decrease the force upon impact during collisions? Give an example
In the momentum -impulse relationship, a decrease in force occurs due to a greater time. When the
contact time is shorter (i.e., quick karate chop), the force is greater
