# P4 Explaining Motion. Equations you need THRUST WEIGHT AIR RESISTANCE Forces on the rocket at T=0 seconds.

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P4 Explaining Motion

Equations you need

THRUST WEIGHT AIR RESISTANCE Forces on the rocket at T=0 seconds

Draw force diagrams for the rocket at T=5s and T=10s THRUST WEIGHT AIR RESISTANCE

Video of a launch http://www.cbsnews.com/video/watch/?id=4 173117n http://www.cbsnews.com/video/watch/?id=4 173117n (please note there is a short delay before the video plays)

Height

TO think about What is the height of the rocket after.. a)5s b) 15s c)25s d) What would happen to the height at 45secs?

Thrust

Explain how the thrust changes with time. Explain why the rocket doesn’t need more fuel?

Air Resistance

How long does it take for air resistance to become zero? Explain why air resistance gets less as the time from launch increases.

Calculations What is the GPE at the maximum height the rocket reaches assuming no weight loss from burning the fuel GPE = mgh = 90N x 3750 = 337500j (3375Kj) (remember weight in Newtons is a force which is mass x gravity) Assuming no air resistance as the rocket returns to Earth calculate the velocity of the rocket from this height KE =GPE = 1/2mv 2 = 33750Kj = ½ x 0.9Kg x v 2 v 2 = 33750Kj / 0.45 = 750000 V= √750000 = 866m/s

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