Tuesday, 9/30: Friction

Due 10/1: HW: Friction

Bryttani and Marco are fighting over a box of chocolates sitting on a table. Bryttani is pulling the box of chocolates to the right with a force of 8N. Marco is pulling the box to the left with a force of 7.5N. The box of chocolates has a mass of 0.2 kg and a coefficient of kinetic friction of 0.2
A. Calculate the friction on the box. Which direction is it?

B. Draw a free body diagram of the box of chocolates. Remember to include all forces exerted on the box.

C. Find the net force on the box in the horizontal (x) direction.

D. Find the acceleration of the box in the horizontal direction.

E. If the box started from rest (v_ox= 0), how far will it travel in 2 seconds? Which way?

Monday, 9/29: Tug-of-War

In class today we talk about the physics behind tug-of-war and we go outside to play. Let's face it: this is and excuse to go outside and play tug-of-war :)

But there will be homework, and you are responsible for understanding how Newton's Third Law applies to tug-of-war. Specifically, how can anyone win if when you tug back on the rope, it pulls you with an equal force forward? It seems like no team should be able to win...

Assigned: HW: Net Force and Acceleration
Due: HW: Newton's Third Law: Action-Reaction Force Pairs

Notes: Click to enlarge. Remember, these notes are available at school in the class notebook.

Due 9/30: HW: Net Force and Acceleration

Assigned: 9/29. Due: 9/30

One side of this homework has free body diagrams for which you find the net force on each body. Unfortunately, I cannot post that here. But the other side has this series of questions:

Ale and Ernesto are fighting over a box of chocolates sitting on a table. Ale is pulling the box of chocolates to the right with a force of 8N. Ernesto is pulling the box to the left with a force of 7.5N. The box of chocolates has a mass of 2 kg (why can’t they just share? That’s a lot of chocolate!).

A.Draw a picture of this situation. Remember to label everything and everybody, including which way you’re calling positive.

B.Draw a free body diagram of the box of chocolates. Remember to include all forces exerted on the box.

C.Find the net force on the box in the horizontal (x) direction.

D.Find the acceleration of the box in the horizontal direction.

E.If the box started from rest (vox= 0), how far will it travel in 2 seconds? Which way?

Due 9/29: HW: Newton's Third Law: Action-Reaction Force Pairs

For each action force described below, write the reaction force that completes the pair.

1. A man pushes a box to the right.
2. A woman pulls a sled north.
3. A snake pulls a bird down.
4. A monkey pulls down on a tree branch.
5. A swimmer pushes backwards on the water.
6. The Earth pulls down on you.

9/26: Newton's 3rd Law

Click to enlarge. Remember, these notes are available at school in the class notebook.

Due 9/26: HW: Newton's 2nd Law

1. What is meant by net force? Draw a diagram as part of your answer.

2. Suppose a cart is being moved by a certain net force. If the net force is doubled, by how much does the cart’s acceleration change?

3. How much force does a 20,000 Kg rocket need to have an acceleration of 1 m/s²?

4. If a 1N net force accelerates a 1 kg mass at 1 m/s², what is the acceleration caused by a net force of 2 N on a 2 kg mass?

5. A certain force applied to a 2 kg mass accelerates the mass at 3 m/s². How much acceleration will the same force make on a 4 kg mass?