Atwoods System Practice

What is the magnitude of net force acting on the three-block system? Assume no friction.

• mg

• 3mg

• 4mg

• 5mg

What is the total mass of the system?

• 4m

• 5m

• 9m

• 14m

Assume no friction. This system is released. A student says, "the 4m block gains kinetic energy but the m block loses kinetic energy." Do you agree?

• Yes

• No

If the mass of the 2m block was doubled (but F is kept constant), what would happen to the acceleration of the system?

• It would be cut in half

• It would decrease, but not by half

• It would double

• It would increase, but not by double

Which of the following is a correct derivation for acceleration? Assume no friction.

• F / 3m

• 2F / 3m

• 2F / 5m

• F / 5m

These blocks are made of the same material. If the floor is rough and the blocks experience kinetic friction as they slide to the right, will the two blocks experience the same or different amounts of frictional force?

• 3m will experience more friction force

• 2m will experience more friction force

• Both blocks experience the same amount of frictional force

• It depends on their surface area

Answer explanation

It does not depend on their surface area. Since they are the same material, they will have the same coefficient of friction. That means it comes down to their normal force, since:

F_fk = μF_N

The 3m block has a greater normal force than the 2m block.

Both blocks are connected by a rope and then an applied force, F, is applied to the 3m block. How does the tension force acting on the 2m block compare to the tension force acting on the 3m block?

• Greater on 3m because it has a greater mass

• Greater on the 2m because it is being dragged

• Equal and opposite due to Newton's third law

• Depends on whether the blocks are experiencing frictional force

This system is released but does not move. What is the magnitude of static friction experienced by the 9m block?

• 3mg Newtons

• 9mg Newtons

• 14mg Newtons

• Cannot be determined without μ

Answer explanation

If the system is not moving, then all the forces must be balanced. There is an unbalanced net force of 3mg from the hanging block's forces of gravities. So, if we are at rest, that 3mg of force must be balanced by 3mg of static friction.

Blocks X and Y are initially at rest. Then, a student applies a force of F_A to the blocks. Eight seconds later, block Y has a velocity of 40 m/s. What is the system's acceleration, in m/s²?

Mathematical Equivalence

ON

Blocks X and Y start at rest. A teacher pulls to the right with an unknown force on the blocks. Some time later, block X has travels 8 meters and ends up with a velocity of 24 m/s. What is the system's acceleration, in m/s²?

Mathematical Equivalence

ON

Answer explanation

v² = v₀² + 2a(Δx)

24² = 0² + 2a(8)

576 = 16a

a = 36 m/s²