A spring has a spring constant of 800 N/m. How much work must be done to stretch the spring 0.4 m from its unstretched position? A. 64.0 J
B. 160.0 J
C. 320.0 J
D. 640.0 J

We put a force of 50n on an object and the acceleration is 100 m/s². what is the mass of the object?

The ratio of lift to drag l/d for a wing or airfoil is an important aerodynamic parameter, indeed, it is a direct measure of the aerodynamic efficiency of the wing. if a wing is pitched through a range of angle of attack, l/d first increases, then goes through a maximum, and then decreases. consider an infinite wing with an naca 2412 airfoil. estimate the maximum value of l/d. assume that the reynolds number is 9x10^6.

The mass of the sun is 1.99×1030kg and its distance to the earth is 1.50×1011m. what is the gravitational force of the sun on the earth?