I think I got these right, but I'd feel better if someone could tell me if I did them correctly:(adsbygoogle = window.adsbygoogle || []).push({});

A projectile is launched from ground level at a 45 degree angle. How much work does gravity do on the projectile between its launch and when it hits the ground?

Gravity will do as much work on the object as the work performed by the

y-component of the force that launched the projectile.

[tex]

W_{gravity} =\Delta K_{gravity}

\]

\[

\Delta K_{gravity} =\frac{1}{2}mv_y^2

\]

\[

\Delta K_{gravity} =\frac{1}{2}m\left( {\sin (45)v} \right)^2

\]

\[

W_{gravity} =\frac{1}{2}m\left( {\sin (45)v} \right)^2

[/tex]

A hockey player pushes a puck of mass 0.50 kg across the ice using a constant force of 10.0 N over a distance of 0.50 m. How much work does the hockey player do? If the puck was initially stationary, what is its final speed? (Ignore friction.)

[tex]W=Fd, W=10N*0.5m, W=5N[/tex]

[tex]

F=ma

\quad

\Rightarrow

\quad

a=\frac{F}{m}

\]

\[

a=\frac{10.0N}{0.50kg}

\quad

\Rightarrow

\quad

a=\frac{10.0\rlap{--} {k}\rlap{--} {g}\cdot m/s^2}{0.50\rlap{--}

{k}\rlap{--} {g}}

\]

\[

a=20m/s^2

\]

\[

v_f^2 =v_i^2 +2a\Delta d

\quad

\Rightarrow

\quad

v=\sqrt {v_i^2 +2a\Delta d}

\]

\[

v=\sqrt {\left( {2\cdot 20\frac{m}{s^2}} \right)\cdot 0.50m}

\]

\[

v=4.5m/s

[/tex]

If a constant force F=(30.N)i, + (50.N)j acts on a particle that undergoes a displacement (4.0m)i + (1.0m)j , how much work is done on the particle?

[tex]

W=Fd

\]

\[

W=\sqrt {\left( {3.0N} \right)^2+\left( {5.0N} \right)^2} \cdot \sqrt

{\left( {4.0m} \right)^2+\left( {1.0m} \right)^2}

\]

\[

W=20J

[/tex]

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# Homework Help: Check my answers please (3 work questions)

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