Exam 4 Forces in 1 Dimension

A 5 kg block is pulled across a horizontal surface with a force of 30 N and moves at constant velocity. What is the magnitude of the frictional force acting on the block?

• 5 N

• 15 N

• 30 N

• 45 N

Answer explanation

Since the block moves at constant velocity, the net force is zero. Therefore, the frictional force must equal the applied force of 30 N, making the magnitude of the frictional force 30 N.

Tags

NGSS.HS-PS2-1

A person in an elevator feels lighter than usual. Which of the following could explain this?

• The elevator is moving downward at a constant speed.

• The elevator is accelerating downward.

• The elevator is accelerating upward.

• The elevator is at rest.

Answer explanation

The person feels lighter because the elevator is accelerating downward. This reduces the normal force acting on them, making them feel less weight.

Tags

NGSS.HS-PS2-1

If a block is in equilibrium, the magnitude of the block's acceleration is

• 
  zero

• 
  decreasing

• increasing

• 
  constant, but not zero

Answer explanation

If a block is in equilibrium, the net force acting on it is zero, which means there is no acceleration. Therefore, the magnitude of the block's acceleration is zero.

Tags

NGSS.HS-PS2-1

Which of the following blocks has the greatest inertia?

• A 1 kg block moving at 10 m/s

• A 2 kg block at rest

• A 5 kg block moving at 2 m/s

• A 4 kg block accelerating at 1 m/s²

Answer explanation

Inertia is related to mass. The 5 kg block moving at 2 m/s has the greatest mass, thus the greatest inertia, compared to the other options which have less mass or are at rest.

On planet Z, a 60 kg object weighs 240 N. What is the acceleration due to gravity on planet Z?

• 4 m/s²

• 9.8 m/s²

• 6.0 m/s²

• 8.0 m/s²

Answer explanation

To find the acceleration due to gravity, use the formula: weight = mass × gravity. Here, 240 N = 60 kg × gravity. Solving for gravity gives 240 N / 60 kg = 4 m/s². Thus, the acceleration due to gravity on planet Z is 4 m/s².

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NGSS.HS-PS2-4

If a net force causes a 4 kg block to accelerate at 10 m/s², what is the acceleration of an 8 kg block under the same force?

• 2.5 m/s²

• 5.0 m/s²

• 10 m/s²

• • 20 m/s²

Answer explanation

Using Newton's second law, F = ma, the same net force on an 8 kg block results in a lower acceleration. Since F = 4 kg * 10 m/s² = 40 N, for the 8 kg block: a = F/m = 40 N / 8 kg = 5.0 m/s².

Tags

NGSS.HS-PS2-1

Which object is in equilibrium?

• 
  Earth orbiting the Sun

• 
  a thrown baseball at its highest point above the ground

• a car moving at a constant speed in a straight line

• 
  a bicycle skidding to a stop in a straight line

Answer explanation

A car moving at a constant speed in a straight line is in equilibrium because the forces acting on it are balanced, resulting in no acceleration. The other options involve changes in motion or forces.

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NGSS.HS-PS2-2

When the sum of all the forces acting on a block is zero, the block

• 
  must be at rest

• 
  must be accelerating

• 
  may be slowing down

• 
  may be moving at constant speed

Answer explanation

When the sum of all forces is zero, the block is be in equilibrium, which means it can either be at rest OR moving at constant speed. Thus, the correct choice is that it may be moving at constant speed.

Tags

NGSS.HS-PS2-1

A rock is thrown straight up into the air. At the highest point of the rock's path, the magnitude of the net force acting on the rock is

• 
  less than the magnitude of the rock's weight, but greater than zero

• 
  greater than the magnitude of the rock's weight

• 
  the same as the magnitude of the rock's weight

• 
  zero

Answer explanation

At the highest point, the rock's velocity is zero, but gravity still acts on it. The net force is equal to the weight of the rock, which is the only force acting on it, making the net force the same as the magnitude of the rock's weight.

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NGSS.HS-PS2-4

A 2.64-kilogram object weighs 25.9 newtons on Earth. If the acceleration due to gravity on Mars is 3.71 meters per second² , what is the object's mass on Mars?

• 2.64 kg

• 3.71 kg

• 9.79 N

• 25.9 N

Answer explanation

The mass of an object remains constant regardless of location. Therefore, the object's mass on Mars is the same as on Earth, which is 2.64 kg.

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NGSS.HS-PS2-1

NGSS.HS-PS2-4