(4.) The magnitude of the vector sum of two vectors a and b is 8u, and magnitude of b is 5u. If the direction of a is reversed, the magnitude of the vector sum becomes 10u. Find the angle between a and b

The experiment done in lab is repeated, using a ball that has unknown mass m. you plot your data in the form of f 2 versus m/l, with f in rev/s, m in kg, and l in m. your data falls close to a straight line that has slope 3.19 m/(kg · s2). use g = 9.80 m/s2 and calculate the mass m of the ball.