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Projectile physics homework

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At t = 0, an object is projected with a speed v0 = 35 m/s at an angle q0 = 20.6° above the horizontal. For parts a-g, calculate the requested quantities at t = 10 s into the flight. (Use 9.81 m/sec2 for g.)

a) The vertical acceleration of the object:
I got -9.8 m/s2

b) Its horizontal acceleration:
I got 0 m/s2 for this one.

c) Its vertical velocity:
I dont know how to start this. I thought it would be 35sin(20.6), but its not.

d) Its horizontal velocity:
vx = m/s *
I got 32.76 m/s for this one.

e) The angle to the horizontal at which the object is traveling (an angle above the horizontal should be reported as a positive number; an angle below the horizontal should be reported as a negative number). Please give your answer in degrees:
angle = °

For this one, I'm assuming you need the answer to c and d, but I only have d.

f) Its vertical displacement, from where it started:
g) Its horizontal displacement, from where it started:

For f and g, I think you use vf=vi + at, right?

h) At what time does the object reach its maximum height?
 

Answers and Replies

  • #2
rock.freak667
Homework Helper
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At t = 0, an object is projected with a speed v0 = 35 m/s at an angle q0 = 20.6° above the horizontal. For parts a-g, calculate the requested quantities at t = 10 s into the flight. (Use 9.81 m/sec2 for g.)

a) The vertical acceleration of the object:
I got -9.8 m/s2
This is correct.

b) Its horizontal acceleration:
I got 0 m/s2 for this one.
Correct.

c) Its vertical velocity:
I dont know how to start this. I thought it would be 35sin(20.6), but its not.
35sin(20.6) is the initial vertical velocity (i.e. velocity at t=0), you want the velocity at t=10. So what equation relates final velocity, initial velocity acceleration and time?

d) Its horizontal velocity:
vx = m/s *
I got 32.76 m/s for this one.
This is correct. (assuming you did 35cos20.6, since I don't have a calculator to check that)

e) The angle to the horizontal at which the object is traveling (an angle above the horizontal should be reported as a positive number; an angle below the horizontal should be reported as a negative number). Please give your answer in degrees:
angle = °
When you get the vertical velocity at t=10, then you should see that the vertical and horizontal components at t=10 form a right angled triangle. You can use the tangent function to get the required angle.
 
  • #3
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You're almost correct for "C." You've got a solid start. 35sin(20.6) is its INITIAL vertical velocity. Once it begins travelling upwards, however, it begins to slow down. Use the equation [tex]v=at+v_{0}[/tex]. Use 35sin(20.6) as your v0 value, and take into account the acceleration due to gravity.

For f and g, use another kinematics equation, [tex]x=x_{0}+v_{0}t+\frac{1}{2}at^{2}[/tex].

For h, use that same equation, [tex] v=at+v_{0} [/tex]. Plug in the values of "a" and "v0" and go from there.
 

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