Science Quarter 2

A 75-kg astronaut floating in space throws a 5-kg rock at 5 m/sec. How fast does the astronaut move backwards?

-25 m/sec

The rate at which speed changes.

Acceleration

The slope of a speed vs. time graph is equal to the object's ________.

Acceleration

9.8 m/sec2

Acceleration due to gravity "g"

During a race, you speed up from 3 m/sec to 5 m/sec in 4 seconds. What is your change in speed? What is your acceleration?

2 m/sec 0.5 m/sec2

A car accelerates from 0 to 20 m/sec in 10 seconds. Calculate its acceleration.

2 m/sec2

During a science experiment, your teacher drops a tennis ball out of a window. The ball hits the ground 3 seconds later. What was the ball's speed when it hit the ground? Ignore air resistance.

29.4 m/sec

What is the net force required to accelerate a 1,000 kg car at 3 m/sec?

3,000 N

Aya's mass is 45 kg. What is her weight in newtons on Earth?

441 N

You pull your little cousin in a wagon. You must pull with a net force of 50 N to accelerate her at 2 m/sec2. What's her mass?

50 kg

How fast does a 1000 kg car have to move to have a momentum of 50,000 kg-m/sec?

50 m/sec

Idil's momentum is 110 kg-m/sec when she walks at 2 m/sec. What's her mass?

55 kg

What is the momentum of a 2-kg ball traveling at 4 m/sec?

8 kg-meters/sec

By home much does the speed of an object in free fall change each second?

9.8 m/sec

Slope

Divide rise by run.

Explain how to calculate the slope of a graph.

Divide the rise by the run of the line.

Explain how to calculate the slope of a line.

Divide the rise by the run. Or find the area of the triangle/rectangle.

You know mass and acceleration and want to find force.

F=ma

Relates force, mass, and acceleration in the equation F=ma

Newton's Second Law

According to __________, for every action force, there is a reaction force equal in strength and opposite in direction.

Newton's Third Law

The slope of a position vs. time graph is equal to an object's ______.

Speed

What does the slope of a position vs. time graph represent?

Speed

How can you use a speed vs. time graph to find an object's acceleration?

Take the change in speed (rise) and divide it by the change in time (run).

Why don't action and reaction forces cancel?

The forces act on different objects.

Explain the law of conservation of momentum and how is relates to Newton's third law.

The law states that the total momentum in a system of interacting objects cannot change as long as all forces act only between the objects in the system. The total momentum of the two interacting objects stays constant due to the third law.

An astronaut carries a rock from the moon to Earth. Is the rock's mass the same on Earth as on the moon? Is its weight the same?

The mass is the same because mass is constant anywhere in the universe. The weight is different because weight depends on gravity, and there is less gravity on the moon.

What is the difference between mass and weight?

The mass of an object will be the same anywhere in the universe. Since weight is the force of gravity on an object, an object's weight will be different on the moon than it is on Earth.

Describe the motion of a freely falling object. Use the words speed, acceleration, and distance in your answer.

The motion of a freely falling object is an object in acceleration due to the force of gravity with no other forces acting on it. The object will accelerate at a speed of 9.8 m/sec2; so it moves a greater distance each second.

An object accelerates if its speed changes. What is they other way an object can accelerate (without changing speed).

The object can change direction.

A book rests on a table. The force of gravity pulls down on the book. What prevents the book from accelerating downward?

The reaction force of the table.

Which has more momentum: a 50-kg truck moving at 10m/sec or a sports car with a mass of 1,200-kg moving at 50 m/sec?

The sports car

Why don't action and reaction forces cancel?

They act on different objects.

Speed with direction

Velocity

What is the difference between speed and velocity?

Velocity is speed and direction, while speed is just speed.

The force of gravity on an object

Weight

You and your little cousin are standing on inline skates. You push off of each other and both move backwards. a.) Which one of you moves back at a greater speed?

Your little cousin, who has less mass than you (hopefully).

You know mass and force and want to find the acceleration.

a=F/m

A ball is thrown straight up into the air. As it moves upward, its speed _________ by _____ each second. As if falls back down, its speed _________ by __ each second.

decreases 9.8 m/sec increases -9.8 m/sec

You know force and acceleration and want to find the mass.

m=F/a

The mass of an object multiplied by its velocity equals its __________.

momentum

Action and reaction forces always have the ______ strength and act in _________ directions.

same different