Physics Forces Quiz 05

An object that experiences a net force of 80 Newtons speeds up from 10 m/s to 20 m/s over a period of 5 seconds. What is the mass of the object?

• 8 kg

• 40 kg

• 160 kg

• 800 kg

• 1600 kg

Answer explanation

To find the mass, use Newton's second law: F = ma. The acceleration (a) is (20 m/s - 10 m/s) / 5 s = 2 m/s². Rearranging gives m = F/a = 80 N / 2 m/s² = 40 kg. Thus, the mass of the object is 40 kg.

Tags

NGSS.MS-PS2-2

What will happen to an object if a force that opposes its motion is greater than the force pushing or pulling it forward?

• The object will move slower and slower the entire time.

• The object will move at constant speed for a while and then slow down.

• The object will slow down for a while and then move at constant speed.

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

Answer explanation

When a force opposing an object's motion is greater than the force propelling it, the object will decelerate continuously. Thus, it will move slower and slower the entire time until it stops.

Tags

NGSS.MS-PS2-2

Which of the following statements is TRUE if a moving object is slowing down?

• A force within the object must be decreasing.

• A force that is pulling or pushing the object forward must be decreasing.

• A force that is causing the object to slow down must be greater than the sum of the forces that are pulling or pushing the object forward.

• A force that is causing the object to slow down must be increasing.

Answer explanation

When an object is slowing down, the force opposing its motion must be greater than the forward forces. This means the force causing the slowdown is dominant, confirming that it must be greater than the sum of the forward forces.

Tags

NGSS.MS-PS2-2

An empty cart is put into a launcher and pushed with a force F. Then, the same cart is launched with a force 2F (or twice as big). What is the difference in the motion of the cart?

• It depends on the friction of the turning wheels of the cart.

• Both pushes produce the same motion; the size of the push does not matter.

• The bigger push produces a greater change in the cart's speed.

• There is no difference because the bigger push produces greater friction.

Answer explanation

The bigger push (2F) results in a greater change in the cart's speed due to Newton's second law (F=ma). A larger force leads to a larger acceleration, thus increasing the speed more than the smaller force (F).

Tags

NGSS.MS-PS2-2

When Billy gets home from school he begins to push objects around on his air hockey table. He wants to know what affects the change in speed of the objects on the frictionless surface. Choose the statement below that is the most accurate.

• You can make an object go faster if you push it harder for the same amount of time.

• Since the air hockey table is frictionless, when you push objects with the same force for the same amount of time, they will move with the same speed.

• If you push an object harder it will go faster, regardless of the length of time that you push it.

Answer explanation

The correct choice states that pushing harder for the same time increases speed. This aligns with Newton's second law, where greater force results in greater acceleration, thus increasing the object's speed on a frictionless surface.

Tags

NGSS.MS-PS2-2

How much net force does it take to make a 20 kg object accelerate at a rate of 5 m/s/s?

• 0.25 N

• 4 N

• 25 N

• 40 N

• 100 N

Answer explanation

To find the net force, use Newton's second law: F = m * a. Here, m = 20 kg and a = 5 m/s². Thus, F = 20 kg * 5 m/s² = 100 N. Therefore, the correct answer is 100 N.

Tags

NGSS.MS-PS2-2

A school bus is slowing down as it comes to a stop sign. Which of the following statements is TRUE about the forces acting on the school bus while it is slowing down but still moving forward?

• As long as the school bus is still moving forward, the forward force of the school bus has not run out.

• As long as the school bus is still moving forward, any forces moving it forward would have to be larger than any forces slowing it down.

• If the school bus is slowing down, any forces moving it forward would have to be smaller than any forces slowing it down.

• If the school bus is slowing down, any forces moving it forward would have to be the same size as any forces slowing it down.

Answer explanation

If the school bus is slowing down, it means the forces acting against its motion (like friction) are greater than the forces propelling it forward. Therefore, the forward forces must be smaller than the forces slowing it down.

Tags

NGSS.MS-PS2-2

Mildred drops the 3-kg steel puck and the 1-kg aluminum puck at the same time from the same height. she observes that the pucks land at the same time. How does the force on the steel puck compare to the force on the aluminum puck?

• The force on the steel puck must be 3 times bigger since the steel puck had three times the mass.

• The force on the aluminum puck must be 3 times bigger since the steel puck had three times the mass.

• The force is the same on both pucks since gravity made the two pucks fall at the same rate.

• We cannot determine the forces without knowing the actual values for mass and acceleration.

Answer explanation

The force on the steel puck is greater because force is calculated as mass times acceleration (F=ma). Since the steel puck has three times the mass of the aluminum puck, its force must also be three times greater.

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-4

The following Velocity vs. Time graph represents the motion of an object. When does the object have a net force acting in the opposite direction of the motion?

• From A to B

• From A to C

• From B to C

• Never; the speed is constant

• Never; the acceleration is constant

Answer explanation

From A to B, the velocity decreases, indicating a net force acting in the opposite direction of motion. This is because the object is decelerating, which means the force is opposing its motion.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

The Position vs. Time graph represents the motion of an object. When does the object have a net force acting in the same direction as the motion?

• From A to B

• From B to C

• From C to D

• From D to E

• From A to B and C to D

Answer explanation

The object has a net force acting in the same direction as the motion from A to B, as indicated by the increasing position. This means the object is accelerating in that interval.

Tags

NGSS.MS-PS2-2