EMPA

An object experiences a uniform circular motion in a horizontal plane, as illustrated to the right. The direction of the net force is:

• a

• b

• c

• d

• e

When a car makes a turn what kind of force do the seat belts make on you?

• linear force

• 1. circular force

• centripetal force

• the seat belts do not exert a force on you, you  exert a force on the seat belt.

When an object experiences uniform circular motion, the direction of the net force is

• in the same direction as the motion of the object.

• in the opposite direction of the motion of the object.

• is directed toward the center of the circular path.

• is directed away from the center of the circular path. 
  

An object moves in a circular path at a constant speed.  Compare the direction of the object's velocity and acceleration vectors.

• Both vectors point in the same direction.

• The vectors point in opposite directions.

• The vectors are perpendicular.

• The question is meaningless, since the acceleration is zero.

When a car rounds a curve on a flat road what supplies the centripetal force that keeps the car moving in a circular path?

• Static friction

• Kinetic friction

• normal force

• tension forcetension force

6. A pilot executes a vertical dive then follows a semi-circular arc until it is going straight up.  Just as the plane is at its lowest point, the force on him is

• less than mg, and pointing up.

• less than mg, and pointing down.

• more than mg, and pointing up

• more than mg, and pointing down

Universal Gravity: 

Two objects are attracted to each other by a gravitational force F. If one mass is doubled and one mass is quadrupled without changing the distance, what is the new gravitational force between the objects in terms of F?

• 2 F

• 4 F

• 6 F

• 8 F

Two objects are attracted to each other by a gravitational force F. If both masses are doubled without changing the distance, what is the new gravitational force between the objects in terms of F?

• 4 F

• 2 F

• ½ F

• ¼ F

A spacecraft starts on Earth is moving to Mars. Which of the following is correct about the gravitational force on the spacecraft due to Earth’ attraction?

• The force becomes zero when the spacecraft is half way between the planets

• The force becomes zero when the spacecraft is closer to the surface of Mars

• The spacecraft is never beyond the Earth’s gravitational attraction

• The force becomes zero when the spacecraft land on the surface of Mars

The earth’s orbit around the sun is approximately circular. What is the direction of the net force on the earth?

• Towards the sun.

• In the direction of its velocity.

• Opposite the direction of its velocity.

• Away from the sun.