Physics, Chapter 4

What is the net force acting on a falling 1 kg ball if it encounters 2N of air resistance?

A 1 kg ball has a weight of (1 kg * 10 m/s 2), which is equal to 10 N. Air resistance is a force in the opposite direction to a falling weight so the net force acting on the ball is 10 N - 2 N = 8 N.

A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.

moving with a constant nonzero acceleration Since there is a net force acting, the body does not move at a constant velocity, but it accelerates instead. However, the force acting on the body is constant. Hence, according to Newton's 2nd law of motion, the acceleration of the body is also constant.

A 1-kg stone and a 10-kg stone have the same acceleration in free fall because _______.

the ratio of weight to mass is the same for each.

A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion?

It could be moving to the left, moving to the right, or be instantaneously at rest. The acceleration of an object tells you nothing about its velocity--the direction and speed at which it is moving. In this case, the net force on (and therefore the acceleration of) the block is to the right, but the block could be moving left, right, or in any other direction.

Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?

Terminal speed must be higher to make air drag equal the gravity force for a heavier person.

What is the acceleration of a falling object that has reached its terminal velocity?

The acceleration is 0. WHY?

What two principal factors affect the force of air resistance on a falling object?

The force depends mostly on frontal area and speed.

An object cannot remain at rest unless which of the following holds?

The net force acting on it is zero. If there is a net force acting on a body, regardless of whether it is a constant force, the body accelerates. If the body is at rest and the net force acting on it is zero, then it will remain at rest. The net force could be zero either because there are no forces acting on the body at all or because several forces are acting on the body but they all cancel out.

If a block is moving to the left at a constant velocity, what can one conclude?

The net force applied to the block is zero. If there is a net force acting on a body, regardless of whether the body is already moving, the body accelerates. If a body is moving with constant velocity, then it is not accelerating and the net force acting on it is zero. The net force could be zero either because there are no forces acting on the body at all or because several forces are acting on the body but they all cancel out.

What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance?

The net forces are 6 N and 0 N, respectively.

Two forces, of magnitude 4N and 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________.

cannot have a magnitude equal to 5N WHY?