3. You are on the target range preparing to shoot a new rifle when the range saf

Question

3. You are on the target range preparing to shoot a new rifle when the range safety officer comes up to you and asks you what the muzzle velocity is of your rifle. (Muzzle velocity is the velocity at which the bullet leaves the rifle's barrel.) You say, "I don't know, but let's find out." You bring the rifle up to shoulder level and aim it horizontally at the center of the target, which is 50 m away. You then carefully squeeze off a shot at the target. The range safety officer announces to everyone to secure their firearms and retrieve their targets. When you collect your target, you find that your bullet hit the target at a point 9.5 cm below where you aimed. What was the muzzle velocity? 4. In 1989, Lee Wheelis of Luling, TX set the world record for longest watermelon seed spit. He spit a watermelon seed a distance of 20.96 m. a) Assuming that he spit the watermelon seed at an angle of 45°, what was the initial velocity of the seed? b) What was the maximum height above the ground reached by the seed during it's flight? Assume that he spit the seed from ground level and that you can neglect air resistance. 5. A rocket is launched straight upward starting from rest. It accelerates at a constant acceleration of 50 m/s? for a period of t seconds. At this time, the rocket engine has run out of fuel, so the rocket "coasts" upward for a period of t2 seconds until it reaches an altitude of 7000 m. At 7000 m altitude, the upward velocity of the rocket is 0 m/s, so the rocket starts falling back towards the ground. Neglecting air resistance, find t1, the period of time the rocket was accelerating, and 12, the period of time the rocket was coasting upward. 6. I recently dreamt that our class met on the surface of an alien planet. I took my trusty billiard ball and dropped it from a height of 8 m. The class found that it took 1.7 s for the ball to hit the planet's surface. Then, I let the ball roll down a I m long track that was inclined at an angle of

Explanation / Answer

5.

consider the accelerated motion of rocket during first t1 seconds

a = acceleration = 50 m/s2

Vo = initial velocity = 0 m/s

t1 = time of travel = ?

Y1 = displacement

Vf1 = final velocity after time t1

Using the equation

Vf1 = Vo + at

Vf1 = 0 + 50 t

Vf1 = 50 t1 eq-1

Using the equation

Y1 = Vo t1 + (0.5) a t12

Y1 = 0 t1 + (0.5) (50) t12

Y1 = 25 t12 eq-2

consider the motion during t2 seconds

Vo = initial velocity = Vf1 = 50 t1

Y2 = displacement

Vf = final velocity = 0

Using the equation

Vf2 = Vo2 + 2 a Y2

02 = (50 t1 )2 + 2 (-9.81) Y2

Y2 = 127.6 t12 eq-3

Using eq-1 and eq-2

Y1 + Y2 = 7000

25 t12 + 127.6 t12 = 7000

t1 = 6.8 sec

using equation

Vf = Vo + at2

0 = 50 t1 + (-9.8) t2

t2 = (5.1) (6.8) = 34.7 sec

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