# Tutor profile: Doreen J.

## Questions

### Subject: Swahili

How do you say "what time is it in Swahili"?

Ni saa ngapi?

### Subject: Physics

A race car going around a flat, unbanked circular track gradually increases speed as it completes one full trip around the track. Which of the following can explain why the car gains speed? (A) Energy stored in the fuel is converted to mechanical energy. (B) A component of the frictional force exerted by the ground on the tires is directed toward the center of the circle. (C) A component of the frictional force exerted by the ground on the tires is in the direction of motion. (D) The car's velocity and acceleration are perpendicular.

The choices A and C are correct. A is correct because fuel is burned in order to cause the car to move forward and C is correct because the frictional force in the direction of motion allows the tires to turn.

### Subject: Calculus

For F(x,y) = xe^((x^2)y), find fx and fy, and evaluate each at the point (1, ln 2).

Since fx(x,y) = xe^((x^2)y)*(2xy) + e^((x^2)y), the partial derivative of f with respect to x at (1, ln 2) is e^(ln 2)*(2 ln 2) + e^(ln 2) = 4 ln 2 + 2. Since fy(x,y) = xe^((x^2)y)*(x^2) = (x^3)*(e^((x^2)y), the partial derivative of f with respect to y at (1, ln 2) is e^(ln 2) = 2.

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