Forces

The person in the picture wants the crate to move to the right at 4.0 m/s. A friction force of 9.0 N to the left is acting on the crate as it slides. The person needs to pull to the right with a force of ---.

• 4.0 N

• 9.0 N

• 13.0 N

• anything more than 9.0 N

Answer explanation

"To move to the right at 4.0 m/s" is a velocity that is constant. A constant velocity means an acceleration of zero, so the forces must add up to zero (in the horizontal direction).

Tags

NGSS.MS-PS2-2

According to the free-body diagram of the engine block being dragged across the floor, this engine block is ---.

• moving to the right

• not moving

• accelerating to the right

• cannot say without more information

Tags

NGSS.MS-PS2-2

What is happening to the rocket in the picture?

• It is being accelerated down

• It is moving down

• It is moving up

• It is being accelerated up

Tags

NGSS.HS-PS2-1

Select ALL of the items below which could be represented by the arrow shown above for a car moving in a circular path as seen from above.

• centripetal force

• linear velocity (a.k.a. tangential velocity)

• angular velocity

• centripetal acceleration

A car with mass m travels around a curve with velocity v. What do you know about the centripetal force if the speed triples?

• Nothing

• The centripetal force triples

• the centripetal force multiplies by 9

• The centripetal force divides by 3

A dolphin swims in a circle with a radius of 30 m and moves with a speed of 3.2 m/s. What is the dolphin’s centripetal acceleration?

• 0.341 m/s²

• 0.106 m/s²

• 96 m/s²

• 307.2 m/s²

Tags

NGSS.HS-PS2-1

A carnival ride is being designed to move a ride vehicle in a circle at a particular speed. If the design is changed so that the radius is one-third as big, and the speed is one-half as much, the new acceleration will be --- times the original design acceleration.

• 3/2

• 2/3

• 3/4

• 4/3

Answer explanation

Apply the Rule of Ones for $\frac{v^2}{r}$ so you do $\frac{\left(\frac{1}{2}\right)^2}{\frac{1}{3}}$

Tags

NGSS.HS-PS2-1

The direction of the net force on an object moving in a circular path is ---.

• outward, because that's the direction it feels like it's being pulled

• forward, because that's the direction of the velocity

• inward, because that's which way it gets pulled to keep it from flying off in a tangent line path

• forward, because that's the direction of the acceleration

Two massive bodies are pulling on each other with gravity with a force of 12.0 µN. If one object is replaced with another object six times as massive, and the distance is changed to four times the original distance, the new force will be ---.

• 4.5 µN

• 18.0 µN

• 288 µN

• 0.375 µN

Answer explanation

Apply the Rule of Ones to the gravitational force: $G\cdot\frac{m_1\cdot m_2}{d^2}$ so you get  $1\cdot\frac{6\cdot1}{4^2}=\frac{6}{16}=\frac{3}{8}$  and multiply this by the original 12.0-µN force

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-4

Two objects are attracted to each other with 36 N of gravitational force.

What would the force between them be if the distance between them were doubled?

• 9 N

• 18 N

• 72 N

• 144 N

Tags

NGSS.MS-PS2-4