## Force examples

10/12/2010

3 Comments

Force, Mass, Acceleration, Weight, Gravity

REMEMBER: A weight is a special case of force.

example 1: what is the mass of a 200. kg object?
200. kg

example 2: what is the weight of a 200. kg object?

weight = mass x gravity
200. kg x 9.8 m/s2 =
1960 kg m/s2 =
1960 newtons

example 3: what is the mass of a 200. newton object?
mass = weight / gravity
200. kg m /s2 / 9.8 m/s2 =
20.4 kg

example 4:  A little boy pushes a wagon with his dog in it. The mass of the dog and wagon together is 45 kg. The wagon accelerates at 0.85 m/s2. What force is the boy pulling with?

m = 45 kg
a = 0.85 m/s^2
F = ?
F = ma

F = (45 kg)(0.85 m/s^2)
F = 38.25 N

## Comments

10/13/2010 6:50pm

hey ms.j this is Taylor how are you i was wondering are we still having a test tommorow?

matthew
10/13/2010 10:26pm

Mrs. James

this is the first problem. a runner has a mass of 89 kilograms. he produces a force of 84 newtons between the ground and his running shoes. how fast does he accelerate? can you please tell me the steps to work out this problem. i am not sure where to start.

C James
10/14/2010 4:36pm

@Matthew,

F= ma
so divide each side by mass to get acceleration by itself and you will get

a= F/m

then write out your knowns

F= 84 N
m= 89 kg
a= ?

substitute the numbers for the variables

a= 84 N/ 89 kg
a= 0.94 n/kg

remember that a Newton (N) is equal to kg(m/s^2)

so you have 0.94 (kg*m/s^2)/kg
the kg will cancel and you will have only the m/s^2 left leaving you with the answer

0.94 m/s^2 I hope you get this let me know