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2-6 Application of the equation of motion

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1 2-6 Application of the equation of motion

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

3 Sketch vi Vf xi Xf Δx=xf-xi a

4 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.

5 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?

6 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?

7 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

8 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

9 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?

10 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?

11 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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