Physics Forces Quiz 04

Chris sends a heavy cart and a light cart at the same speed across the lab table. How did the starting push on each cart compare?

• The more massive cart needed a bigger push because both mass and force affect motion.

• The lighter cart needed a bigger push because the friction force is larger for an object with less mass.

• Both pushes are the same because they are both on the same surface and experience the same frictional force.

• Both pushes were about the same size because force, not mass, affects motion.

Answer explanation

The more massive cart needed a bigger push because greater mass requires more force to achieve the same acceleration, according to Newton's second law of motion (F=ma). Thus, the heavier cart needs a larger initial push.

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Is it possible for an object to move at constant speed without a force pulling or pushing it?

• Yes, an object will move at constant speed as long as the force inside the object doesn’t run out.

• No, a force is needed to keep an object moving at constant speed, but it doesn’t have to be a constant force.

• Yes, an object will move at constant speed unless a force acts to change its motion.

• No, a constant force is needed to keep an object moving at constant speed.

Answer explanation

Yes, an object will move at constant speed unless a force acts to change its motion. This aligns with Newton's first law, which states that an object in motion stays in motion unless acted upon by an external force.

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The arrows labeled WIND and WATER represent forces acting on a sailboat during a certain period of time. During this period of time, the force of the wind on the sailboat is stronger than the force of the water on the sailboat. The directions of the arrows show the directions of the forces, and the lengths of the arrows represent the strengths of the forces. Which statement best describes the sailboat's motion while these forces are acting?

• The sailboat will move at constant speed the entire time.

• The sailboat will speed up for a short time and then move at constant speed.

• The sailboat will speed up for a short time and then slow down.

• The sailboat will speed up the entire time.

Answer explanation

Since the force of the wind is stronger than the force of the water, the sailboat will experience a net force in the direction of the wind. This means the sailboat will continuously speed up as long as these forces are acting.

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The graph shows the net force (sum of all the forces) on a block during different time intervals as you move the block across a table. When is the block moving at constant speed?

• From 0 to 2 minutes

• From 2 to 4 minutes

• From 4 to 6 minutes

• From 0 to 2 and from 4 to 6 minutes

Answer explanation

The block moves at constant speed when the net force is zero. From 4 to 6 minutes, the graph shows no net force, indicating constant speed. Other intervals show varying forces, meaning acceleration.

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The Position vs. Time graph represents the motion of an object. When does the object have a net force acting on it?

• From A to B and then from B to C but not at time B.

• From A to C

• From A to B

• From B to C

• Never; the speed is constant.

Answer explanation

The correct choice is 'Never; the speed is constant.' A Position vs. Time graph with a straight line indicates constant speed, meaning no net force is acting on the object throughout the motion.

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NGSS.MS-PS2-2

The Velocity vs. Time graph represents the motion of an object. When does the object have a net force acting on it?

• From A to B and then from B to C but not at time B.

• From A to B

• From A to C

• From B to C

• Never; the speed is constant.

Answer explanation

The object experiences a net force when its velocity changes. From A to C, the velocity is not constant, indicating a net force is acting on the object throughout this interval.

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A 60 kilogram physics student would weigh 1560 newtons on the surface of planet X. What is the magnitude of the acceleration due to gravity on the surface of planet X?

• 0.038 m/s/s

• 6.1 m/s/s

• 9.8 m/s/s

• 26 m/s/s

Answer explanation

To find the acceleration due to gravity (g), use the formula: weight = mass × g. Here, 1560 N = 60 kg × g. Solving for g gives g = 1560 N / 60 kg = 26 m/s². Thus, the correct answer is 26 m/s/s.

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A net force of 10 Newtons accelerates an object at 5.0 meters per second per second. What net force would be required to accelerate the same object at 1.0 meter/sec/sec?

• 1.0 N

• 2.0 N

• 5.0 N

• 50.0 N

Answer explanation

Using Newton's second law, F = ma, we find the mass (m) of the object: m = F/a = 10 N / 5 m/s² = 2 kg. To accelerate at 1 m/s², F = ma = 2 kg * 1 m/s² = 2 N. Thus, 2.0 N is required.

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A man pushes on a 70 kg crate with a force of 420 Newtons.The box accelerates at a rate of 5 m/s/s. What is the net force on the crate?

• 6 N

• 14 N

• 84 N

• 350 N

• 420 N

Answer explanation

To find the net force, use Newton's second law: F_net = mass × acceleration. Here, F_net = 70 kg × 5 m/s² = 350 N. The net force on the crate is 350 N.

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NGSS.MS-PS2-2

Object A is twice as massive as Object B. Both objects are at rest. A net force of five newtons is applied to both objects. Which of the following statements best describes their resulting motion?

• Object A will accelerate half as much as Object B because it has twice the mass.

• Object A will accelerate twice as much as Object B because it has twice the mass.

• Their motion will be the same because the same net force was applied to both.

• Neither object will move at all. There needs to be unbalanced force applied to make them move.

• It is not possible to tell from the information given. Five Newtons may not be enough net force to make either object move.

Answer explanation

According to Newton's second law (F=ma), Object A, being twice as massive, will have half the acceleration of Object B when the same force is applied. Thus, Object A will accelerate half as much as Object B.

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