Anonymous asked in Science & MathematicsPhysics · 2 months ago

Help! 3 part physics assignment?

Doing rough in AP physics. I really can’t seem to get this. 

A ball of mass m,initially at rest , is kicked directly toward a fence from a point D meters away, as shown above. The velocity of the ball as it leaves the kicker's foot is v, at an angle above the horizontal The top of the fence is H meters high. The ball hits nothing while in flight and air resistance is negligible .

a. write an equation for the time (t) it takes for the ball to reach the plane of the fence

b.will the ball hit the fence? justify your answer 

c. sketch the horizontal and vertical components of the velocity of the ball as functions of time until the ball reaches the plane of the fence

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2 Answers

  • NCS
    Lv 7
    2 months ago
    Favorite Answer

    a) the horizontal velocity is constant, so

    x = v*cosΘ*t = 20m/s*cos37º * t = 16m/s * t

    b) time to hit the fence t = x / v*cosΘ = 32m / 16m/s = 2.0 s

    height at that time:

    h = vsinΘ*t + ½at² = 20m/s*sin37º*2s - ½*9.8m/s²*(2.0s)²

    h = 4.4 m

    It looks like your fence is 2.5 m high (very blurry). If so, then the ball clears the fence by 1.9 meters.

    c) To help with the sketch, find the time for the ball to reach its maximum height (and zero vertical velocity):

    t = v*sinΘ / g = 20m/s*0.6 / 9.8m/s² = 1.2 s

    Sketch below.

    If you find this helpful, please select Favorite Answer. You get points too!

    Attachment image
  • oubaas
    Lv 7
    2 months ago

    Vo = 20 m/sec

    Voy = Vo*sin 37° = 20*0.6 = 12.0 m/sec 

    Vox = Vo*cos 37° = 20*0.8 = 16.0 m/sec 

    time t to reach the fence = d/Vox = 32/16 = 2.0 sec

    height h at the fence = Voy*t-g/2*t^2 = 12*2-4.9*2^2 = 24-19.6 = 4.4 m  

    the ball will clear the fence by 4.4-2.5 = 1.9 m 

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