Physics Praxis

According to Newton’s third law of motion, the strength of a reaction force is ____________________ the strength of the action force.

• equal to

• negative to

• positive to

• greater than

Tags

NGSS.MS-PS2-1

The force of gravity is responsible for continuously changing the ____________________ in which a satellite moves.

• direction

• orbit

• centripetal force

• gravitation

Tags

NGSS.MS-ESS1-2

Which of the following represents a correct formula for calculating acceleration?

• a = (v_f - v_i) / t

• a = v_i / t

• a = v_f + v_i * t

Answer explanation

Acceleration is the rate at which velocity changes and is therefore calculated by dividing the change in velocity by time.

Which of the following is an example of Newton's law of inertia?

• The force of a bowling ball on the pins equals the force of the pins on the ball.

• A bowling ball continues rolling down the bowling lane until it strikes the pins

• The weight of a bowling ball is directly proportional to its mass.

• 
  The force on a bowling ball by a person's hand is proportional to its mass and acceleration.

Answer explanation

Newton's law of inertia states that an object in motion will continue in its motion without change unless acted upon by an external force. The ball continues to roll at constant speed until its motion is changed by the pins.

A child pulling a wagon along a sidewalk suddenly notices the wagon is slowing down. If the child continues to pull on the wagon with a forward force of 12 N, which of the following best describes the force of friction on the wagon as it slows?

• greater than 12 N

• equal to 12 N

• 
  less than 12 N

Answer explanation

The force of friction will slow the wagon if the friction force is greater than the forward force. Since the wagon is slowing, the friction force must be greater than the 12 N force of the pull.

Tags

NGSS.MS-PS2-2

According to Newton's law of inertia, which of the following is required for a particle to move at constant speed along a curved path on a frictionless surface?

• an unbalanced force

• an increasing mass

• 
  conservation of momentum

Answer explanation

Newton's law of inertia states that an object tends to resist a change in its motion (including its direction of motion) unless acted upon by an unbalanced external force.

Of the following, which is a statement of Newton's second law of motion?

• An object's acceleration depends on its mass and the net force acting on the object.

• An object's kinetic energy depends on its mass and speed.

• 
  The force of gravity between two objects depends on their masses and the distance between them.

• For every force on one object by a second, there is an equal and oppositely direct force on the second object by the first.

Answer explanation

Newton's second law can be expressed by F = ma, where F is the net force on the object, m is the object's mass, and a is the object's acceleration.

Tags

NGSS.MS-PS2-2

Which of the following activities is the best example of an inquiry-based activity?

• Students are given an assortment of objects made of various materials. Students use magnets to test hypotheses about which materials are magnetic.

• Students describe a magnetic material. Students use a table of properties of magnetic substances and classify various objects as either magnetic or non-magnetic.

• Students read a selection about magnetism in their textbooks. Students work with partners to discuss the selection and answer questions about magnetism,

• Students watch a video about the earth's magnetic field. Students complete a worksheet as they watch the video.

Answer explanation

This activity involves students forming their own hypotheses and testing those hypotheses on their own.

Tags

NGSS.MS-PS1-2

Given the free body diagram below, which arrow represents the force that keeps the box from falling through the ramp?

• a

• b

• c

• d

Answer explanation

Arrow A is the normal force. It is a support force by the ramp on the box and acts in a direction perpendicular to the ramp. The normal force keeps the box from falling through the ramp because it resists the component of gravity that pulls the box into the ramp.

Tags

NGSS.MS-PS2-2

Which of the following best describes the concept of inertia in physics?

• A) The tendency of an object to resist changes in its state of motion

• B) The force required to accelerate an object

• C) The energy stored in an object due to its position

• D) The rate of change of velocity of an object