# Homework Help: How to find net force using mass, distance, and time?

1. Nov 4, 2009

### elkosp16

1. The problem statement, all variables and given/known data[/B]
A 2.0 kg otter starts from rest at the top of a muddy incline 85 cm long and slides down to the bottom in 0.50 s. What net force acts on the otter along the incline?

mass = 2.0 kg
distance = 85 cm
time = .50 s
net force = ?

2. Relevant equations
Fnet=ma

I also used.
V=x/t
a=v/t

3. The attempt at a solution
v=x/t
85/.5=170

a=v/t
170/.5=340 cm/s^2
340 cm/s^2 = 3.4 m/s^2

Fnet=ma
(2.0 kg)(3.4 m/s^2)= 6.8 N

The book says the right answer is 14 N though.

2. Nov 4, 2009

### ApexOfDE

No, velocity is not constant. It changes over time. You should read your textbook again or check this http://en.wikipedia.org/wiki/Equation_of_motion" [Broken] to find appropriate formula.

Last edited by a moderator: May 4, 2017
3. Nov 4, 2009

### Deep_Blue

Hi elkosp16, you need to use the formula :

Δ X = Vi*T + (1/2)*a*T^2

You already know displacement (ΔX), 85 cm (remember to convert it to meters !)
Initial velocity (Vi) is 0, because it starts at rest.
Time = .50 seconds,
Plug everything in and solve for a,

once you get acceleration, use newtons second law.
∑ F=m*a
plug in mass & acceleration, the answer is net force.