Force on Systems

A heavy tractor force FT to push a lighter box. Under which conditions will FB, the force with which the box pushes on the tractor, be equal in magnitude to FT?

• The tractor and box must be at rest.

• The tractor and box must be moving with constant velocity.

• The tractor and box must be either at rest or moving with constant velocity.

• These two forces are always equal in magnitude under all conditions.

Tags

NGSS.HS-PS2-1

Which of the following best explains what a person does in order to jump vertically into the air?

• The person uses her legs to push herself up off of the ground with a force equal to her weight.

• The person pushes down on the floor with a force equal to her weight, causing the floor to exert an upward force on the person equal to her weight.

• The person uses her legs to push herself up off of the ground with a force greater than her weight.

• The person pushes down on the floor with a force greater than her weight, causing the floor to exert an upward force on the person greater than her weight.

Tags

NGSS.HS-PS2-1

Three blocks set at rest on a frictionless surface are connected by identical springs. The rightmost block is acted upon by a constant 20 N force, as shown below, starting at time t = 0. The blocks no longer oscillate after 10 seconds. M3. Which of the following will be true after 10 seconds have elapsed?

• The right spring will be stretched twice as far as the left spring.

• The left spring will be stretched twice as far as the right spring.

• The right spring will store twice as much potential energy as the left spring.

• The left spring will store twice as much potential energy as the right spring.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS3-1

NGSS.HS-PS3-2

Three blocks set at rest on a frictionless surface are connected by identical springs. The rightmost block is acted upon by a constant 20 N force, as shown below, starting at time t = 0. The blocks no longer oscillate after 10 seconds. What is the speed of the center of mass of the system at t = 2 seconds, while the blocks are still oscillating?

• 2 m/s

• 8 m/s

• 10 m/s

• 20 m/s

Tags

NGSS.HS-PS2-1

The diagrams below show three cases in which one or more blocks are set on a frictionless track. The frictionless track has straight and inclined sections separated by a pulley wheel. In Case 1, a 1 kg block is set at rest on the inclined section and has an acceleration of 6 m/s² upon being released.

In Case 2, a 2 kg block is set on the inclined section and released from rest. What acceleration will the 2 kg block have as it slides down the incline?

• 1 m/s²

• 2 m/s²

• 3 m/s²

• 6 m/s²

Tags

NGSS.HS-PS2-1

The diagrams below show three cases in which one or more blocks are set on a frictionless track. The frictionless track has straight and inclined sections separated by a pulley wheel. In Case 1, a 1 kg block is set at rest on the inclined section and has an acceleration of 6 m/s² upon being released.

In Case 3, the 2 kg block is connected to the 1 kg block by a string. The 2 kg block rests on the horizontal section, the 1 kg block is held fixed on the inclined section, and the string passes over the ideal pulley. What acceleration will the system of blocks have the instant that the 1 kg block is released?

• 1 m/s²

• 2 m/s²

• 3 m/s²

• 6 m/s²

Tags

NGSS.HS-PS2-1