Which of the following statements is true? a. a 140-lb. person would weigh more than 140 lbs on the moon because of the increase in gravity. b. earth has a synchronous rotation, when means its rotation and revolution periods are the same length. c. earth's moon is unique because it is larger than any other natural satellite in the solar system. d. leap years add an extra day to february because the earth takes longer than 365 days to orbit the sun.

D. Leap years add an extra day to February because the Earth takes longer than 365 days to orbit the sun.

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.