Physics

An object is dropped from the top of a building and hits the ground 3 seconds after it is released. What is the approximate speed of the object at the instant it hits the ground?

30m/s because it will speed up by approximately 10m/s every second.

Instead of dropping a ball, you throw a ball directly downward. After releasing the ball, what is the magnitude of its acceleration?

9.8m/s^2

You are lying on your back on the slope of a grassy hill, watching the clouds go by overhead. Which is the best statement about the force of friction exerted on you by the ground in this situation?

A force of static friction pointing "uphill", parallel to the surface of the hill, is applied to you by the ground. Frictional forces always act in a direction parallel to the surfaces that are intereacting. Kinetic friction exists between surfaces that are in contact and moving relative to each other.

Which of the following objects is considered to be in free fall?

A hammer that is tossed upward by an astronaut on the moon. An object is in free fall when the only force acting on it is the force of gravity.

This velocity vs. time graph exhibits what kind of motion?

A moving object that is speeding up at a constant rate.

The position vs. time graph exhibits what kind of motion between Q and R?

A moving object that is speeding up.

The motion of two cars A and B is describe with these positions vs. time graph. From these graphs, what can you conclude about the motion of the cars?

Car A is driving at a faster constant speed than car B.

When you drop a ball, what is true about its motion?

It falls and increases in speed at a rate of 9.8m/s every second.

Josh punched his open left hand with his right hand. Which statement is true about the forces his two hands exert on each other?

Josh's right hand and left hand exert equal and opposite forces on each other.

While sparring, Katie punches Arman in the shoulder. Which statement is true about the forces Katie and Arman exert on each other?

Katie exerts a force on Arman's shoulder and Arman exerts a force on Katie's hand.

Miguel leans against a wall. Which statement is true about the forces Miguel and the wall exert on each other?

Miguel and the wall exert equal and opposite forced on each other.

A ball is dropped off a tall building and falls for 6 seconds before landing on the ground. Consider how far the ball falls in its first 3 seconds of free fall compare to how far it falls in its next 3 seconds.

The ball falls farther in the second 3-second interval than it does in the first interval.

When you throw a ball directly upward, what is true about its acceleration?

The ball's acceleration is always directed downward.

In the motion diagram, a car is driving to the right and there are equal time increments between frames. How is the moving?

The car is slowing down.

Blocks A and B have equal masses, and are connected by a rope that passes over a frictionless pulley. At this moment, the system is in motion, with block B moving downward and A moving upward at a constant speed. Compare the magnitudes of the force of tension exerted on block A and the force of tension exerted on block B.

The force of tension exerted on block A is equal in magitude to the force of tension exerted on block B.

Stephanie pulls on a rope that is attached to a large crate. She is pulling the crate along a constant speed as it slides across rough carpet. How does the magnitude of the force of tension exerted on Stephanie compare to the magnitude of the force of tension exerted on the crate?

The force of tension exerted on the crate has the same magnitude as the force of tension exerted on Stepanie.

A hand is pushing on block B to the right, causing both blocks to move to the right across a rough surface at a constant speed. Compare the force that pushed block B to the right to the force that pushed block A to the right.

The force that pushed block A to the right is smaller than the force that pushes block B to the right.

You are standing in an elevator as it starts to move downward, accelerating for a moment. Which is true at that moment?

The net force on you changes from zero to downward as the elevator begins accelerating. If you are accelerating, then your net force must be in the same direction as the acceleration.

Consider a car speeding up as it drives along a level road. Which of the following is an action-reaction pair?

The normal force exerted on the car by the road and the downward force exerted on the road by the car.

This position vs. time graph represents the motion of an object moving in a straight line. What is true about the object's motion?

The object is at rest.

A ball is dropped off of a tall building and falls for 2 seconds before landing on a balcony. A rock is then dropped from the top of the building and falls for 4 seconds before landing on the ground. How does the final speed of the rock compare to the final speed of the ball?

The rock's finl speed is twice as much as the ball's final speed. Becase when an object is dropped from rest in free fall, its speed is directly propostional to the time it has fallen.

Which is the best description of g?

g is the magnitude of the acceleration due to the force of gravity.

A person is trying to pull a heavy create across a room with a rope that is attached to the crate, but it doesn't move. The tension in the rope

is equal at both ends of the rope. If a rope is not accelerating, then the net force on it must be zero.

The mass of an object

is not a vector and has no direction. An object's weight is a force and has a direction associated with it, but the mass is scalar, with no direction at all.

Consider a car at rest, parked on level ground. The force of friction between a car tire and the ground

is zero. There is no friction needed to keep the car in place.

When an object is dropped from rest in free fall, its:

speed is directly proportional to the time it has fallen.

A box rests on a table. The normal force exerted by the table on the box is equal in magnitude to the weight of the box and points in the opposite direction. This is because

the net force on the box is zero, and, therefore, the forces must be balanced.

If an object's acceleration vector points in the same direction as its instantaneous velocity vector then you can conclude

the object is speeding up. Does not experience an acceleration. If the object was at rest or moving at a constant speed, its velocity would not change and it would not have an acceleration at all. If the object was slowing down, then the final velocity would be smaller than the inital velocity and they would have different signs.

To define the position of an object in a plane, you need to measure

the object's distance from a reference point and its angle measured from a reference line.