# Physics Problems Kinematics, Acceleration

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1) A VW RAbbit can go from rest to 80.5 km/h (50.0 mi/h) in a modest 8.20 s. How long will it take to speed from 48.3 km/h to 64.4 km/h, along a straight run, if the average acceleration is the same as before?

2)During a takeoff a small plane has an average tangential acceleration of 5.0 m/s^2 and travels for 20 s before becoming airborne. What is the initial speed of the plane? How long must the runway be?

3)While making a movie a cowboy on a horse rides up to a moving train traveling at 5.0 km/h along a straight length of track. After running next to the last car for a while he charges ahead toward the engine 100 m away and gets there in 1.10 min. Assuming it was constant, determine the scalar value of his acceleration?

4) The acceleration due to gravity on the surface of the Moon is about g/6. If you can throw a ball straignt up to a height of 25 m on Earth, how high would it reach on the Moon when launched at the same speed? Ignore the minor effects of air friction.

5) A small rocket is launched vertically, attaining a maximum speed at burnout of 1.0x10^2 m/s and thereafter coasting straight up to a maximum altitude of 1510 m. Assuming the rocket accelerated uniformly while the engine was on, how long did it fire and how high was it at engine cutoff? Ignore air friction.

6) Imagine that someone dropped a firecracker off the roof of a building and heard it explode exactly 10 s later. Ignoring air friction, taking g = 9.81 m/s^2 and using 220 m/s as the speed of sound, calculate how far the cherry bomb had fallen at the very moment it blew up.

#### Solution Preview

(1) Since the acceleration is considered to be uniform, the difference in velocities is given by the acceleration times the time:

<br>

<br>v2-v1 = a x t

<br>t= (v2-v1)/a= (64.4-48.3)/(80.5/8.2)=1.64 s

<br>where acceleration is calculated based on the initial information. Note that ther's no need to change the units into m/s for this question.

<br>(2) Am I missing something here? Does it ask for the initial velocity or the final? If starting from zero speed, the *final* velocity would be

<br>v=a x t = 100 m/s

<br>And the distance covered would be

<br>x = 1/2 a x t^2 = 500 m

<br>However please check the problem and email brainmass operations if there's any problems, and they'll forward it to me.

<br>(3) We ...