# Homework Help: Roller Coaster Question

1. Oct 13, 2018

### Austin Gibson

1. The problem statement, all variables and given/known data:
A child of mass 40.0 kg is in a roller coaster car that travels in a loop of radius 7.30 m. At point A the speed of the car is 15.0 m/s, and at point B, the speed is 15.6 m/s. Assume the child is not holding on and does not wear a seat belt.

What is the force (in N) of the car seat on the child at point B? (Enter the magnitude.)

2. Relevant equations
Fc = [(mv^2)/r]
Fc = ma

3. The attempt at a solution:

I solved (a) and (c).
I solved (a) by inserting the mass, speed, and radius into the equation [(mv^2)/r] and subtracting by (mass*gravity).
My equation for (b) was [(mv^2)/r * cos30] - mg = [(40*(15.6^2)/7.3*cos30) - (40*9.8) = 762.8 N. That was incorrect. What's improper about my equation?

2. Oct 13, 2018

### SammyS

Staff Emeritus
In what direction is the centripetal force at point B ?

Also, is there any net force on the child at point B ?

3. Oct 13, 2018

### Austin Gibson

120 degrees(90+30)?

4. Oct 13, 2018

### Austin Gibson

I solved it by applying (cos 30) to mg instead of the centripetal force.