Homework 10.21.10

10/21/2010

read pp 136-137 and complete #1-3 section 6B review

Vivian
10/23/2010 9:20am

Isn't it supposed to be 6B and not 7B?

How do you calculate kinetic energy? I looked at the example but it comes out wrong when I calculate it.

Ciara
10/23/2010 9:29am

on the kinetic energy you gave us, the 3page #4. it says.... Rodger Maris swung a bat which had a mass of 2kg. at a velocity of 45m/s How many joules of kinetic energy could he give to the ball?
The formula is... KE= 1/2mv squared... How do you calculate it because it comes out to be 1/2(2kg)(45m/s)... are we supposed to divide 1/2 to (2kg), or multiply (2kg) and (45m/s).. then divide?

C James
10/23/2010 10:57am

@ Vivian, yes it is 6B. I changed it when I entered it but the change did not show up. When I went back to change it the change showed up. Sorry about that. Kinetic energy is calculated by
KE= 1/2mv^2

@Ciara
remember your order of operations first square the velocity then multiply the mass and then divide by 2 see below. Also remember that 1 kg*m^2/v^2 is 1 J

KE= 1/2 mv^2

KE= ?
m= 2 kg
v= 45 m/s

1. KE= 1/2(2 kg)((45 m/s)^2)
2. KE= 1/2(2 kg)(2025 m^2/s^2)
3. KE= 1/2(4050 kg*m^2/s^2)
4. KE= 2025 kg*m^2/s^2
5. KE= 2025 J

Ciara if you notice in step 1 (or 2 or 3) you are multiplying by 2 and dividing by 2 so in this particular problem you could actually cancel the 2s out.

Ladies, let me know if you are having any other problems!!!
God bless
C James

ciara
10/23/2010 2:20pm

Thank you :D i understand now.. :)

Vivian
10/23/2010 2:21pm

Thanks Ms. James!