Solutions to your most recent quiz

#1. a) potential   b) potential    c) kinetic   c) kinetic
#2 Tommy: since Fg = mg = 4.5(9.8) = 44.1 N, so W = Fd (44.1)(0.5) = 22.05 J
     Nancy: zero work since the textbook is motionless
     Cindy: W = 30(4) = 120 J
     Therefore, Cindy spent the most amount of energy, followed by Tommy then Nancy

#3
a) Fg = mg = 24(9.8) = 235.2 N
b) W = Fd = 300 (4.5) = 1350 J
c) Fg is reduced by a third so the new Fg = 235.2/3 = 78.4 N (use answer is part a)
    So W = Fd = 78.4(1.4) = 197.76 J

#4
a) Since 8.2 = m (9.8/6), so m = 8.2/1.63 = 5 kg
    {divide 9.8 by 6 because gravity on the moon is about 1/6 of Earth's}

b) W = Fd = 8.2(1.55) = 12.71 J

c) More energy is required since the rock weighs more (due to stronger gravity on Earth...6 times stronger!). This means that work required on Earth is 6 times that of the moon.

On Earth: W = 8.2(6)(1.55) = 76.26 J
On moon: W = 12.71 J (answer in part b)
Therefore difference in energy spent = 63.55 J

****There are different ways to solving these questions. Also, rounding may have affected certain answers so yours do not need to be an exact match to the above answers.***

Quiz tomorrow (Thursday, Jan. 23)

There will be a pop quiz tomorrow on 4.1 and 4.2 (main concepts are mass, weight, work and energy). Review your notes and worksheets!

Here are some additional practice questions:
1. Determine the force of gravity acting on a 16.5-kg object on Earth's surface.
2. Provide a scenario in which the object in #1 would 'lose' its weight but not its mass. Explain how the weight is reduced in your scenario.
3. Determine the amount of work down by a car engine if it exerts a force of 1000N to move the car a distance of 0.8 km.
4. A backpack was lifted from the floor to be placed on the top shelf of a student's locker. The height of the shelf is 1.6 m. The backpack itself is 0.6 kg and contains 4 heavy textbooks - each with a mass of 1.75 kg. Determine the amount of energy required to move the backpack onto the shelf.

Science Update

Completed Sec. 4.1 and "Force of Gravity" lab

Today and next week: Sec. 4.2 Work and Energy

If you are OR will be away, please make sure you read 4.2 on your own and answer the C&R questions at the end of the section.

Highlight: Mass and Weight

Understanding Mass and Weight

Mass - amount of matter in an object (kg); therefore it remains constant
Weight - amount of gravitational force acting on the object (N); changes depending on gravity

The relationship between m and w on Earth is: 1 kg = 9.8 N      OR    Fg = mg

**pop QUIZ on tomorrow (Friday, Jan. 10)***
[Those of you that are reading this...good for you! You won't be caught off guard tomorrow.]

Welcome back!

Happy New Year, Grade 8s!

We're starting our second unit - Systems in Action this week.
Topic: 4.0 (intro), 4.1: Force
Key concepts: force, mass, weight, gravity