Forces and Motion Review

Luke and Sarah have an assignment to construct an experiment that shows how the amount of force needed to accelerate an object is proportional to its mass. Which answer would BEST describe the motion of the cart, assuming there is no friction?

• The cart will move to the left at a constant speed.

• The cart will move to the right at a constant speed.

• The cart will accelerate (increase speed) to the left.

• The cart will accelerate (increase speed) to the right.

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A student is conducting an experiment to determine what will happen to the gravitation force of two boxes, with different masses, if the boxes are pushed together. One box has a mass of 100 g and the other box has a mass of 150 g. What will happen if these two boxes were moved closer together?

• gravitational force would remain constant

• gravitational force would not be created

• gravitational force would decrease

• gravitational force would increase

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Assuming both players are on the same surface and are wearing the same kind of shoes, who will win the game and why?

• Mason will win because although he is applying less force than William, he is smaller and can move faster than William.

• Mason will win because the unbalanced forces applied by Mason and William will cause William to move toward Mason.

• William will win because the unbalanced forces applied by Mason and William will cause Mason to move toward William.

• William will win because he is applying more force than Mason so he is larger and can mover faster than Mason.

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The Earth and the moon exert a gravitational force on each other. The distance from the Earth to the moon is approximately 240,000 miles.

What would happen to the gravitational force if the moon were moved to a distance of 480,000 miles?

• The gravitational force would be the same because gravity depends on the mass of the Earth and the moon, not the distance between them.

• The gravitational force would be reduced to zero because the moon is twice as far from the Earth.

• The gravitational force would increase by a factor of two because that moon is twice as far away from the Earth.

• The gravitational force would decrease to one-fourth of its current value because the moon is twice as far from Earth.

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If a ball is rolling with 5 pounds of force, how much force will be needed to stop the ball from rolling and why?

• It would take 25 pounds of force to stop the ball from rolling because it takes five times as much force to stop as object.

• It would take 2.5 pounds of force to stop the ball from rolling because it takes half of the amount of force to stop an object.

• It would take 10 pounds of force to stop the ball from rolling because it takes double the amount of force to stop an object.

• It would take 5 pounds of force to stop the ball from rolling because the same amount of force must be used to stop the object.

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A bag of potatoes hangs motionless from a hook.

What forces are acting on the bag of potatoes, and what are their relative magnitudes and directions?

• The force of gravity on the potatoes and the force of the hook. The force of gravity is larger than the force of the hook. The force of gravity points downward and the force of the hook points upward.

• The force of gravity and the force of the bag. The force of gravity is exactly balanced by the force of the bag. The force of gravity points downward and the force from the bag points upward.

• The force of gravity is pulling the potatoes and the bag. The force of gravity is directed downward toward the ground. No other forces are acting on the potatoes.

• The bag is pulling upward on the potatoes. Because the bag is not moving, no other force is acting on the potatoes.

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Patrick was pushing a box across the floor of his room using 5 pounds of force. Then, a friend pushes in the opposite direction, also applying 5 pounds of force.

What will happen to the box and why?

• The box would not move because the forces applied to the box would be balanced.

• The box will be raised because when two equal forces act on an object it will be raised up.

• The box would move in the direction of the force that was applied last because of Newton’s First Law of Motion.

• The box will continue to move in the original direction that it was pushed because you cannot stop an object once it is in motion.

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The illustration shows people pushing farm carts of equal mass. Each person is pushing with an equal force (F) in the direction shown.

How does the acceleration of Cart A compare to the acceleration of Cart B?

• It is twice the magnitude (amount of force), but in the opposite direction of cart B’s acceleration.

• It is twice the magnitude (amount of force) and in the same direction as cart B’s acceleration.

• It is the same magnitude (amount of force), but in the opposite direction of cart B’s acceleration.

• It is the same magnitude (amount of force) and in the same direction as cart B’s acceleration.

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A science teacher dropped a 5.0 kg brick (weight = 50 N) off of the roof of his house and into the swimming pool below. When making contact with the pool, the brick experienced an upward force of 20 N.

Which BEST predicts the motion of the brick once it makes contact with the pool?

• The brick will stop moving, because a force exerted by the water will cause the velocity to decrease.

• The brick will continue to accelerate, because the force of gravity is stronger than the upward force exerted by the water.

• The brick will continue moving at a lower velocity, because the force exerted by the water will cause the velocity to decrease.

• The brick will maintain a constant velocity, because the force of gravity is stronger than the upward force exerted by the water.

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A book is lying still on a table.

Are the forces on the book balanced? Why or why not?

• Yes, because gravity is pulling the book down and the table is pushing the book up.

• Yes, because gravity is pulling the book up and gravity is pushing the book down.

• No, because the force of gravity and the table exert a different amount of force.

• No, because the force of gravity and the table are not of the same magnitude.

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