4. A projectile is fired at a velocity of 70.0m/s at an angle of 35° from the ed

Question

4. A projectile is fired at a velocity of 70.0m/s at an angle of 35° from the edge of a 100.0m high cliff, as in the figure below. It lands on the ground some time t later. Consider the motion from just after it is fired to just before it hits the ground.

a)List all of the known quantities in the x direction.
b)List all of the known quantities in the y direction.
c)List all of the unknown quantities you could determine with the information given.
d)Determine all of the quantities in (c). Show your work.

Explanation / Answer

a)

Vox = initial velocity = 70 Cos35 = 57.3 m/s

Vfx = final velocity at impact = 57.3 m/s

a = acceleration = 0

b)

Voy = initial velocity = 70 Sin35 = 40.2 m/s

a = acceleration = - 9.8 m/s2

Yo = initial position = 100 m

Y = final position = 0 m

c)

t = time

Vfy = final velocity at the time of impact

d)

consider the motion along Y-direction

using the equation

Y = Yo + Voy t + (0.5) a t2

0 = 100 + 40.2 t + (0.5) (- 9.8) t2

t = 10.2 sec

using the equation

Vfy = Voy + at

Vfy = 40.2 + (-9.8) (10.2) = - 59.8 m/s

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