Two equal masses sit at equal distances from the pivot of a uniform seesaw. The system is

Answer: In rotational equilibrium Equal torques on both sides cancel — net torque zero, so rotational equilibrium.

A 25\text{kg} child sits 1.6\text{m} from the pivot. To balance, a 40\text{kg} child must sit at distance

Answer: 1.0\text{m} 25 \cdot 1.6 = 40 \cdot d \Rightarrow d = 40/40 = 1.0\text{m}.

A student applies a force at the rim of a wheel of radius 0.40\text{m} to produce 20\text{N·m} clockwise torque. A second force of 80\text{N} is applied tangentially at the rim counterclockwise. Is th

Answer: No — the counterclockwise torque wins. CCW torque: (0.40)(80) = 32\text{N·m} 20\text{N·m} CW. Net torque is counterclockwise, so not in equilibrium.

AP Physics 1 · Topic 5.5

Rotational Equilibrium and Newton's First Law in Rotational Form Practice

Part of Torque and Rotational Dynamics.(TOP-5.E)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$Two equal masses sit at equal distances from the pivot of a uniform seesaw. The system is$
- A
  $Rotating clockwise$
- B
  $In rotational equilibrium$
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- C
  $Rotating counterclockwise$
- D
  $About to tip$
Why
$Equal torques on both sides cancel — net torque zero, so rotational equilibrium.$
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Sample 2difficulty 2/5
$25~\text{kg}$
- A
  $1.5~\text{m}$
- B
  $2.5~\text{m}$
- C
  $1.0~\text{m}$
  check_circle
- D
  $0.5~\text{m}$
Why
$25 \cdot 1.6 = 40 \cdot d \Rightarrow d = 40/40 = 1.0~\text{m}$
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Sample 3difficulty 2/5
$0.40~\text{m}$
- A
  $No — the counterclockwise torque wins.$
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- B
  $No — the clockwise torque wins.$
- C
  $Cannot tell without the wheel's mass.$
- D
  $Yes — both torques are equal.$
Why
$(0.40)(80) = 32~\text{N·m}$
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Sample 4difficulty 2/5
$40~\text{kg}$
- A
  $30~\text{kg}$
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- B
  $53~\text{kg}$
- C
  $40~\text{kg}$
- D
  $20~\text{kg}$
Why
$m_1 g d_1 = m_2 g d_2 \Rightarrow m_2 = (40)(1.5)/2.0 = 30~\text{kg}$
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Sample 5difficulty 3/5
$For the previous setup, scale <strong> A </strong> reads$
- A
  $125~\text{N}$
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- B
  $50~\text{N}$
- C
  $175~\text{N}$
- D
  $100~\text{N}$
Why
$300~\text{N}$
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