# Tutor profile: John M.

## Questions

### Subject: Physics (Newtonian Mechanics)

What is the maximum speed a car of mass (m) can travel along a flat curve of radius (r) when the coefficient of friction between the tires and the road is (s)?

To start this problem, we will keep the equation for uniform circular motion in mind, this is F=(mv^2)/r. The force in this problem is the force of friction, which points radially toward the center of the curve. This force of friction (f) is equal to f=sn, where n is the normal force which is n=mg, where g is the acceleration due to gravity on earth. This gives us f=smg. Plugging this in for F in the uniform circular motion equation, we obtain smg=(mv^2)/r. The mass (m) cancels and after rearranging we are left with v=sqrt(sgr), where v is the maximum speed the car can travel to make the turn successfully.

### Subject: Biology

What is the difference between homeotherms (endotherms) and poikilotherms (ectotherms)?

Homeotherms are animals that maintain a constant internal body temperature across a range of external temperature. Poikilotherms, on the other hand, are animals whose internal body temperatures vary along with the external temperature of their environment.

### Subject: Anatomy

If a muscle crosses both the knee and hip joints posterior to the joint, what movements will it create?

The muscle would create flexion at the knee and extension at the hip. Knee flexion brings the leg posterior in the sagittal plane while hip extension brings the thigh and leg posterior in the sagittal plane.