7. The radius of Mars is approximately one-half the radius of Earth, and the mass of Mars is approximately one-tenth the mass of Earth. If Earth exerts a gravitational force of
magnitude F on Mars, the magnitude of the gravitational force of Mars on Earth is?
and why
a)
F
b)
2F
c)
10F
d)
5F

For general projectile motion, when the projectile is at the highest point of its trajectory, its acceleration is zero? a)the horizontal and vertical components of its velocity are zero. b) its velocity is perpendicular to the acceleration. c)the horizontal component of its velocity is zero. d)its velocity and acceleration are both zero.