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Conservation of Energy

AP Physics 1· difficulty 2/5

A roller-coaster cart starts from rest at h=20 mh = 20~\text{m}. Using g≈10 m/s2g \approx 10~\text{m/s}^2 and ignoring friction, what is its speed at h=5 mh = 5~\text{m}?

  • A

    17.3 m/s17.3~\text{m/s}

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  • B

    10 m/s10~\text{m/s}

  • C

    15 m/s15~\text{m/s}

  • D

    5 m/s5~\text{m/s}

Explanation

12v2=g(h0−h)=10(15)=150⇒v=300≈17.3 m/s\tfrac{1}{2}v^2 = g(h_0 - h) = 10(15) = 150 \Rightarrow v = \sqrt{300} \approx 17.3~\text{m/s}.

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