A rock is thrown horizontally off of a cliff with a velocity of 20 m/s. The rock lands 60 m from the base of the cliff. How long will the rock be in the air?

The time spent by the rock in air is 3 s.

Explanation:

Given;

initial  horizontal velocity of the rock, u = 20 m/s

horizontal distance traveled by rock, R = 60 m

The the range of the projectile is given by;

R = vt

where;

v is the initial  horizontal velocity of the rock

t is the time spent by the rock in air

t = R/v

t = 60 / 20

t = 3 s

Therefore, the time spent by the rock in air is 3 s.

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.