course Phy 201 Zá‰[¶‡–ñšÑË€¡²Ÿ¡a«œ©¼f…Š¯åassignment #019
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00:30:17 ** STUDENT RESPONSE: x component of the vector = magnitude * cos of the angle y component of the vector = magnitude * sin of the angle To get the magnitude and angle from components: angle = arctan( y component / x component ); if the x component is less than 0 than we add 180 deg to the solution To get the magnitude we take the `sqrt of ( x component^2 + y component^2) **
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RESPONSE --> x=magnitude*cos of theta y=magnitude*sine theta x^2+y^2=z^2 angle= arctan of y/x is x is positive angle=arctan of y/x plus 360 degrees if x is positive and y is negative . self critique assessment: 2
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00:31:15 Explain what we mean when we say that the effect of a force is completely equivalent to the effect of two forces equal to its components.
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RESPONSE --> The components of two forces add up to be the same as the effect of one force . confidence assessment: 1
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00:33:16 ** If one person pulls with the given force F in the given direction the effect is identical to what would happen if two people pulled, one in the x direction with force Fx and the other in the y direction with force Fy. **
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RESPONSE --> One person pulling with a force F in a given direction, the effect is the same as what would happen if two people pulled, one in the x direction and one in the y direction Am confused by this. self critique assessment: 1
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00:39:06 Explain how we can calculate the magnitude and direction of the velocity of a projectile at a given point.
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RESPONSE --> to get the x component=magnitude*cos theta y component=magnitude*sine theta x^2+y^2=z^2 if x is positive, arctan y/x= angle if x is negative, arctan y/x plus 180 deg if x is positive, y is negative arctan of y/x plus 360 deg. confidence assessment: 2
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00:39:50 ** Using initial conditions and the equations of motion we can determine the x and y velocities vx and vy at a given point, using the usual procedures for projectiles. The magnitude of the velocity is sqrt(vx^2 + vy^2) and the angle with the pos x axis is arctan(vy / vx), plus 180 deg if x is negative. **
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RESPONSE --> ok self critique assessment: 3
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00:47:23 Explain how we can calculate the initial velocities of a projectile in the horizontal and vertical directions given the magnitude and direction of the initial velocity.
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RESPONSE --> x component=magnitude*cos(direction) y component=magnitude*sine(direction) confidence assessment: 1
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00:48:28 ** Initial vel in the x direction is v cos(theta), where v and theta are the magnitude and the angle with respect to the positive x axis. Initial vel in the y direction is v sin(theta). **
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RESPONSE --> x direction=v*cos(theta) y direction=v *sin(theta) self critique assessment: 2
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00:48:39 Univ. 8.58 (8.56 10th edition). 40 g, dropped from 2.00 m, rebounds to 1.60 m, .200 ms contact. Impulse? Ave. force?
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RESPONSE --> confidence assessment:
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00:48:48 ** You have to find the momentum of the ball immediately before and immediately after the encounter with the floor. This allows you to find change in momentum. Using downward as positive direction throughout: Dropped from 2 m the ball will attain velocity of about 6.3 m/s by the time it hits the floor (v0=0, a = 9.8 m/s^2, `ds = 2 m, etc.). It rebounds with a velocity v0 such that `ds = -1.6 m, a = 9.8 m/s^2, vf = 0. This gives rebound velocity v0 = -5.6 m/s approx. Change in velocity is -5.6 m/s - 6.3 m/s = -11.9 m/s, approx. So change in momentum is about .04 kg * -11.9 m/s = -.48 kg m/s. In .2 millliseconds of contact we have F `dt = `dp or F = `dp / `dt = -.48 kg m/s / (.002 s) = -240 Newtons, approx. **
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RESPONSE --> self critique assessment:
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00:52:45 Query Add comments on any surprises or insights you experienced as a result of this assignment.
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RESPONSE --> The part about the two force components being equal to one force is confusing to me. Is that the same as when two people are doing forces and you added them up, like on problem 5 : What are x and y the components of the velocity vector obtained when we add the two following velocity vectors: vector A, with x and y components 7.8 m / s and 7.8 m / s, and vector B whose x and y components are 2.9 m / s and 3.6 m / s? self critique assessment: 2
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