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A person of mass 80 kg runs at 5 m/s toward a stationary 20 kg sled. The person jumps and lands on the sled. What is the speed of the person and the sled after the landing?

User Wch
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1 Answer

24 votes
24 votes

Answer:

4 m/s

Step-by-step explanation:

By the conservation of momentum, we can write the following equation


\begin{gathered} p_i=p_f \\ m_1v_(i1)+m_2v_(i2)=(m_1+m_2)_{}v_f \end{gathered}

Where pi is the initial momentum and it is equal to the sum of the mass times the velocity of the person and the sled. pf is the final momentum of the person and the sled.

The sled is initially stationary, so its initial velocity vi2 is 0 m/s.

We need to know the final velocity vf, so solving for vf, we get


v_f=(m_1v_(i1)+m_2v_(i2))/(m_1+m_2)_{}

Now, we can replace m1 = 80 kg, vi1 = 5 m/s, m2 = 20 kg, vi2 = 0 m/s to get


\begin{gathered} v_f=\frac{(80\operatorname{kg})(5\text{ m/s)+(20kg)(0 m/s)}}{80\operatorname{kg}+20\operatorname{kg}} \\ v_f=\frac{400\operatorname{kg}\text{ m/s+0 kg m/s}}{100\operatorname{kg}} \\ v_f=\frac{400\operatorname{kg}\text{ m/s}}{100\operatorname{kg}\text{ m/s}} \\ v_f=4\text{ m/s} \end{gathered}

Therefore, the speed of the person and the sled after the landing is 4 m/s

slp

User Amr Ayman
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