Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!


Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for K-8 and here for K-12.


Answers:
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1. Velocity is the speed and direction of an object.


2. Speed is just a number. Velocity is a number and a direction.


3. Terminal velocity is when something falling cannot gain any more speed because the air resistance pushing up against that something is equal to the force of gravity pulling down on that something.


4. Gravity pulls on them very lightly and they have a lot of air resistance.


5. Gravity pulls pretty hard and they have little air resistance.


6. Gravity pulls the same on both (they weigh the same) but air resistance is much greater with an open parachute. The force of air resistance equals the force of gravity much more quickly with an open parachute so the fall is slower.


For Advanced Students:

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7. Rest


8. Motion


9. Inertia is a quality of an object that determines how difficult it is to get that object to move, to stop moving, or to change directions. Generally, the heavier an object is, the more inertia it has.


10. When the car is moving, everything in the car is moving at the same rate of speed as the car. If the car changes its speed or direction, the drink’s inertia keeps it moving the way it was moving. So if the car changes direction or speed, and the drink is not restrained, nothing will stop the drink from moving in the same direction it was already moving in and spill all over the seat.


11. A tow truck has more mass so it has more inertia. It is harder to stop, change its direction, or get it moving.


12. 2 feet/second downward. Divide 8 feet by 4 seconds to get 2 ft/s. Add the downward to make it a velocity and not just a speed.


13. 6 seconds. Divide 12 feet by 2 ft/s and you get 6.


14. Neither. Remember last lesson? All things drop with the same acceleration. It’s air resistance that effects the top velocity things can reach. On the Moon, feathers fall as fast as bricks.
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Comments

2 Responses to “Answers to Velocity Exercises”

  1. The terminal velocity is figured out from this equation:

    where

    Vt = terminal velocity
    m = mass of the falling object
    g = acceleration due to gravity
    Cd = drag coefficient
    ρ = density of the fluid through which the object is falling
    A = projected area of the object

    So the terminal velocity for a tennis ball:

    m = 57 grams = 0.057 kg (this is the mass, not the weight, of the tennis ball)
    g = 9.81 m/s2 (this is the same value for all objects falling to the Earth)
    Cd = 0.50 (you need to figure this out for each particular object)
    ρ = 1.2 kg / m3 (this is the density of air at standard temperature)
    A = (3.14)(0.067 m)2 = 0.0141 m2 (this is the area that the wind sees)

    Terminal velocity for a tennis ball = 11.5 m/s (meters per second) = 25.7 mph (miles per hour)

  2. Can you tell me how to calculate the terminal velocity of an object please?

    Thanks,

    Kurt