# 2-6 Application of the equation of motion

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2-6 Application of the equation of motion

Solving problem Draw sketch diagram - label all known quantities
- note what quantities is asking 2. Write down known variable & unknown variable

Sketch vi Vf xi Xf Δx=xf-xi a

Problem 43 A cheetah can acceleration from rest to 25.0 m/s within 6.22 s. Assuming constant acceleration, (a) how far has the cheetah run in this time? (b) After sprinting for 3.11 s, is the cheetah’s speed 12.5 m/s, more than 12.5 m/s, or less than12.5 m/s? Explain (c) What is the cheetah’s average speed for the first 3.11 s of its sprint? For the second 3.11 s of its sprint. (d) Calculate the distance covered by the cheetah in the first 3.11 s, and the second 3.11 s.

Ex 2-8 A park ranger driving on a back country road suddenly sees a deer “frozen” in the headlights. The ranger, who is driving at 11.4 m/s, immediately applies the brakes and slows with an acceleration of 3.80 m/s2. If the deer is 20.0 m from the ranger’s vehicle when the brakes are applied, how close does the ranger come to hitting the deer? How much time is needed for the ranger’s vehicle to stop?

Catching a speeder Speeder 40 mi/hr (17.9 m/s) pass parked police car, Police begin present at an accelerate of 4.5 m/s2. How long to catch the speeder ? How far have the two cars travelled? Velocity of the police when it catch the speeder?

2-7 Freely Falling Objects
Free Fall: falling freely under the influence of gravity. Gravitational acceleration: g=9.8 m/s2, always positive value Set up the y-axis upward as y increasing direction, acceleration a=-g=-9.8 m/s2

Free fall: dropped from rest vi =0 thrown downward vi ≠ 0
thrown upward Vi=0 or vi≠0 vf vi v=0 vf vi Vf

Ex1. Drop a ball for a 3.00m height (a) How long to reach the ground? (b) What is the speed to reach ground? Ex2. A ball is throw straight up at vi=20 m/s, (a) how far does it get to its maxima height? (b) How long does it time? (c) Where is the ball after 3 s? (d) How long does it take back?

Ex3. Throw up a ball in the air vi=10 m/s when does it reach a height of 1m. what is maximum height? Ex4. 2 cars A cop car is at rest and a car speeder at 40 m/s, the cop starts to accelerate at 5 m/s2 (a) How long does it take to catch car? (b) How far?

Ex5. Problem 51 A rocket blast off and moves straight upward from the launch pad with constant acceleration. After 3.0s the rocket is at a height of 80 m. (a) What are the magnitude and direction of the rocket’s acceleration? (b) What is its speed after 12 s?

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