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Ilya [14]
3 years ago
6

A girl, moving at 8.8 m/s on in-line skates, is overtaking a boy moving at 4.3 m/s as they both skate on a straight path. The bo

y tosses a ball backward toward the girl, giving it speed 11.4 m/s relative to him. What is the speed of the ball relative to the girl, who catches it?
Physics
1 answer:
BabaBlast [244]3 years ago
6 0

Answer:16.5 m/s

Explanation:

Given

Velocity of boy(v_b)=4.3 m/s

velocity of girl(v_g)=8.8 m/s

velocity of ball relative to boy(v_{Bb})=11.4 m/s backward

Now We have to find velocity of ball relative to girl

Representing it in vector form

v_b=4.3\hat{i}

v_g=8.8\hat{i}

v_{Bb}=-11.4\hat{i}

and

v_{Bb}=v_B-v_b

v_B=v_{Bb}+v_b

v_B=-11.4\hat{i}+4.3\hat{i}=-7.1\hat{i}

therefore velocity of ball relative to girl

v_{Bg}=v_B-v_g=-7.1\hat{i}-8.8\hat{i}=-16.5\hat{i}

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Answer:

a. 572Btu/s

b.0.1483Btu/s.R

Explanation:

a.Assume a steady state operation, KE and PE are both neglected and fluids properties are constant.

From table A-3E, the specific heat of water is c_p=1.0\ Btu/lbm.F, and the steam properties as, A-4E:

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Using the energy balance for the system:

\dot E_{in}-\dot E_{out}=\bigtriangleup \dot E_{sys}=0\\\\\dot E_{in}=\dot E_{out}\\\\\dot Q_{in}+\dot m_{cw}h_1=\dot m_{cw}h_2\\\\\dot Q_{in}=\dot m_{cw}c_p(T_{out}-T_{in})\\\\\dot Q_{in}=44\times 1.0\times (73-60)=572\ Btu/s

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\dot m_{steam}=\frac{\dot Q}{h_{fg}}\\\\\dot m_{steam}=\frac{572}{1007.8}=0.5676lbm/s

Entropy generation in the heat exchanger could be defined using the entropy balance on the system:

\dot S_{in}-\dot S_{out}+\dot S_{gen}=\bigtriangleup \dot S_{sys}\\\\\dot m_1s_1+\dot m_3s_3-\dot m_2s_2-\dot m_4s_4+\dot S_{gen}=0\\\\\dot m_ws_1+\dot m_ss_3-\dot m_ws_2-\dot m_ss_4+\dot S_{gen}=0\\\\\dot S_{gen}=\dot m_w(s_2-s_1)+\dot m_s(s_4-s_3)\\\\\dot S_{gen}=\dot m c_p \ In(\frac{T_2}{T_1})-\dot m_ss_{fg}\\\\\\\dot S_{gen}=4.4\times 1.0\times \ In( {73+460)/(60+460)}-0.5676\times 1.6529\\\\=0.1483\ Btu/s.R

Hence,the rate of entropy generation in the heat exchanger. is 0.1483Btu/s.R

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slega [8]

Answer:

Explanation:

Here's what we know because it was given to us:

a = -9.8 m/s/s and

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Here's what we know because we rock physics:

v₀ = 0 (because the object was held still before it was dropped).

Here's the equation that ties all that info together in a single one-dimensional equation:

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Filling in and solving for v:

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