Circular Motion

AP Physics 1· difficulty 2/5

On a frictionless surface, blocks AA (2 kg2~\text{kg}) and BB (3 kg3~\text{kg}) are in contact. You push AA with a 20 N20~\text{N} horizontal force so both accelerate together. What is the contact force that AA exerts on BB?

  • A

    20 N20~\text{N}

  • B

    12 N12~\text{N}

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  • C

    8 N8~\text{N}

  • D

    4 N4~\text{N}

Explanation

System: a=20/5=4 m/s2a = 20/5 = 4~\text{m/s}^2. Isolating BB: contact force =mBa=(3)(4)=12 N= m_B a = (3)(4) = 12~\text{N}.

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