Forces & Motion
Two ladies each have a mass of 45 kg. They step into an elevator with a mass of 200 kg. When the elevator begins to move, it has an upward acceleration of 2 m/s2. What is the net force acting on the elevator as it accelerates?
580N
A 3000 kg automobile accelerates at 1 m/s2 and a 300 kg motorcycle accelerates at 10 m/s2. Which of the two moving objects has the greatest force acting on it?
Both have the same force acting on them.
Describe the motion of an object that has a non-zero net force acting upon it.
It is accelerating.
Which object would have the greatest inertia: a slow moving locomotive or a fast motorcycle?
slow moving locomotive
Draw a FBD of an object in equilibrium. What is the motion of the object?
Force up = force down, force to the right = force to the left. Fnet = 0, forces balanced. Moving at constant velocity or at rest.
If the sign of the velocity is positive & the sign of the acceleration is positive, what is the direction of the object's motion & is it speeding up or slowing down?
positive direction & speeding up
If a football with a mass of 5 kg has a net force of 15N acting on it to the left, what will be the acceleration of the football?
3 m/s2 to the left
What are the two types of forces? Give an example of each.
-contact (push, pull, friction, tension)
-field (electric, gravity, magnetism)
What is the definition of inertia?
Inertia is the tendency of an object to maintain its state of motion.
Draw a FBD of a car moving along a flat road accelerating to the right. Include friction.
Balanced Fg down & FN up; big Fa to the right & smaller Ff to the left.
If the sign of the velocity is positive & the sign of the acceleration is negative, what is the direction of the object's motion & is it slowing down or speeding up?
positive direction & slowing down
How much force is required to make a 10 kg mass accelerate at 2.2 m/s2 to the right?
22N to the right
What is the definition of force?
A force causes an acceleration or a change in object's motion.
What is Newton's 3rd Law of Motion? Give an example.
For every action force there is an equal and opposite reaction force.
Example:a rocket, jet airplane, helicopter, a tennis racket hitting a ball etc.
Draw the FBD of an object in free-fall with air resistance.
Fg longer arrow down & Fair resistance shorter arrow up
A net force acting on a 10 kg box produces an acceleration of 3 m/s2. What acceleration will the same net force cause on a 5 kg box?
6 m/s2
Draw the forces acting on a 100N physics student sitting on a lab table.
Student - 100N Fg - downward; 100N FN force from the lab table on the student - upward
Identify the situation when the net force on an object can be zero?
When an object is at rest or is moving at a constant velocity.
Forces cause an object to accelerate and the object's mass resists acceleration. Which of Newton's Laws of Motion is this?
2nd Law of Motion; F=ma
A car has the following forces acting on it: 875N to the right, 4500N to the left, 12,000N up and 13,500N down. What is the normal force acting on the car? Is the car accelerating? Why? What is the magnitude of the net force on the car?
12,000N up; it is accelerating as the forces are not balanced; 3923N
If the sign of the velocity is negative & the sign of the acceleration is negative, what is the direction of the object's motion & is it slowing down or speeding up?
negative direction & speeding up
If the drag force (air resistance) on an airplane is equal to the applied force from the engines, describe the motion of the airplane.
The airplane is at rest or traveling at constant speed.
Is force a vector or scaler? Why?
vector, it has a magnitude & a direction
What is the property of a object that is most related to its' inertia?
mass
An airplane has a 4000N force to the right, a 2000N force to the left, a 9500N force upward, & a 9210N force downward; what is the gravitational force, what is the net external force in the y and x directions, & what is the magnitude of the net external force?
9210N; 290N up; 2000N right; 2021N