Newton's Second Law of Motion - Force and Acceleration

Calculate the horizontal force that must be applied to produce an acceleration of 1.8 g for a 1.2-kg puck on a horizontal friction-free air table.

1.8 = f/1.2 f = 2.16N

How much force does a 20,000-kg rocket develop to accelerate 1 m/s2?

20,000N

Calculate the horizontal force that must be applied to a 1-kg puck to make it accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.

9.8 = f/1 f = 9.8N

Distinguish between force and pressure.

Force - is any influence that tends to accelerate an object; push or pull Pressure - the amount of force per square inch

Suppose a cart is being moved by a certain net force. If the net force is doubled, by how much does the cart's acceleration change?

If the net force is doubled then the acceleration will double as well. Force causes acceleration; if the force to move an object is doubled it will cause the acceleration to double.

What is the cause of friction, and in what direction does it act with respect to the motion of a sliding object?

The cause of friction is the irregularities on the surface of two objects coming into contact with each other. Friction will move in the direction to oppose motion.

If the force of friction acting on a sliding crate is 100N, how much force must be applied to maintain a constant velocity? What will be the net force acting on the crate? What will be the acceleration?

The force can be the same and have a constant velocity, and in such a case the net force is zero so there is no acceleration.

All other things being equal, why does a heavy sky diver have a terminal speed greater than a light sky diver? What can be done so that the terminal speeds are equal?

The heavier sky diver has a greater terminal speed because the greater the weight, the more effective they're able to plow through the air. To equal the terminal speed of the divers they need to be in close proximity, and the heavier diver needs to be spread like a flying squirrel while the lighter diver falls head/feet first.

What is meant by the net force that acts on an object?

The sum of the forces acting on a object minus the sum of the force acting in the opposite direction.

How much air resistance acts on a 100-N bag of nails that falls at its terminal speed?

The terminal speed occurs when the air resistance equals the weight of the bag of nails, in this case it must equal 100N, so the air resistance is 100.

Suppose a cart is being moved by a certain net force. If a load is dumped into the cart so its mass is doubled, by how much does the cart's acceleration change?

When the mass doubles due to a load being added to the empty cart it will cause the acceleration will decrease by one half.

Calculate the acceleration of a 300,000-kg jumbo jet just before takeoff when the thrust for each of its four engines is 30,000N.

a = (30,000/300,000) x (4) = 0.4m/s2

Which produce more pressure on the ground, a person standing up or the same person lying down?

A person standing up has more pressure on the ground than when a person is lying down.

Distinguish between the relationship that defines acceleration and the relationship that states how it is produced.

Acceleration is when an object has a change I motion and acceleration is produced when force is used to change the velocity.

Why d a coin and a feather fall with different accelerations in the presence of air?

Air resistance diminishes the net force on objects and it counteracts the weight of the feather; when the air resistance equals the weight of the feather then net force will become zero and acceleration stops. Air resistance barley affects the coin's acceleration and doesn't equal its weight to cancel its acceleration until it falls for a certain amount of time at a certain sped.

Distinguish between the concepts directly proportional and inversely proportional. Support your statement with examples.

Directly proportional means that something is changed equally as another object. An example would be when net force doubles then acceleration does too; that means they are directly proportional to each other. Inversely proportional means that a whole value is the inverse of another value. An example would be that a mass of an object being doubled would result in the acceleration being a half.

State Newton's second law in words and then in the form of an equation.

Newton's second law - the acceleration produced by a net force on an object is directly proportional to the magnitude of the net force; is inversely proportional to the mass of the object. Acceleration ~ net force/mass

What's the net force acting on a 25-N freely falling object? What's the net force when the object encounters 15N of air resistance? When it falls fast enough to encounters 25N of air resistance?

The net force of the freely falling object is 25N. 25 - 15 = 10N. When encountered with air resistance (15N) the 25N is reduced to 10N. The net force will be zero because 25N of resistance affecting 25N on an object balances each other out.

How do the air resistance and the weight of a falling object compare when terminal speed is reached?

The terminal speed is reached when the weight of an object and the air resistance equal each other causing the net force to be zero so no further acceleration occurs.

Calculate the acceleration of a 2,000-kg, single-engine airplane just before takeoff when the thrust of its engine is 500N.

a = 500/2,000 = 0.25m/s2

a) Calculate the acceleration if you push with a 20-N horizontal force on a 2-kg block on a horizontal friction-free air table. b) What acceleration occurs if the friction force is 4N?

a) a = 20/2 = 10m/s2 b) a = 16/2 = 8m/s2