Answers to Acceleration Exercises

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. Acceleration is the rate at which velocity is changing. In other words, it is the rate speed and/or direction is changing.

2. Yes, it changed speed and you could say it accelerated negatively since it lost speed. (Remember, there’s no such thing as deceleration in physics.)

3. Yup, did I get you with that one? I get most folks. The Moon is not changing speed but it is constantly changing direction.

4. A force is a push or a pull on something.

5. A lot of force is needed to get an object with a lot of inertia moving.

6. Force causes acceleration which is a change in motion (slowing down, speeding up or changing directions).

7. It speeds up. That something is accelerating because there is a net positive force of 1 Newton. The force of gravity is greater then the force of friction.

8. The force of friction is acting on your bike, slowing you down.

9. 10 Newtons. Any less and you slow down, any more and you speed up. If the net forces equal zero, acceleration is zero, so there is no change in speed.

10. Every action has an equal and opposite reaction.

11. You can throw the wrench so that it goes in the opposite direction of the ship. The force of the throw will have an opposite force on you and you will zip to the ship. See how handy physics is?!

12. Newton’s Second. The heavier head of the hammer has a larger mass. The larger mass with the same acceleration will hit with a greater force on the nail then the lighter hammer will. F=ma

13. Newton’s Third Law. Every action has an equal and opposite reaction. The action of the fire extinguisher firing will have an equal and opposite reaction which zips Dave backwards down the hall.

14. Newton’s First Law. An object in motion tends to stay in motion. An object at rest tends to stay at rest. Since I was moving, I continued moving even though the bike stopped. Luckily, my face broke my fall! (Helmets are a good idea!)

15. Gravity and Friction are two ever present forces on this planet that cause things to stop moving. If these forces did not exist, there would be nothing to stop objects from moving all over the place.

For Advanced Students:

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1. d=1/2 at² = 1/2 3ft/s2(4s)² = 1.5ft/s2(16s²) = 24 ft

2. d=1/2 at² ==> 50ft=1/2 a(10s)² ==> 50ft=1/2 a(100s²) ==> 50ft/100s²=1/2 a ==> .5ft/s²=1/2 a ==> 1ft/s²=a

3. F=ma ==> 10N =20kg(a) ==> .5m/s² =a

4. F=ma ==> 20N=40kg(a) ==> .5m/s²=a

5. F=ma ==> F=30kg(5m/s²) ==> F=150 N

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