Which of the following describes an object in static equilibrium? a. a platypus lies motionless on the sand. b. a tuna speeds up from 2 m/s to 3 m/s c. a dolphin jumps out of the water d. a zebra shark swims at a constant speed of 8 m/s

A).  A platypus lies motionless on the sand.

Explanation:

As we know that equilibrium is defined as the system in the state of ZERO net force or zero acceleration condition.

So equilibrium is of two types

1) Static equilibrium : Here object will remain at rest and do not have any type of motion.

2) Dynamic equilibrium : Here object may move with constant speed in same direction so it will not have any acceleration.

So here

B.A tuna speeds up from 2 m/s to 3 m/s

C.A dolphin jumps out of the water

Not in equilibrium as speed is changing so acceleration is not zero

D.A zebra shark swims at a constant speed of 8 m/s

It is in dynamic equilibrium case where speed is constant

so correct answer will be

A.A platypus lies motionless on the sand.

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.

answer a fan shaped mass of sediment deposited at the base of a mountain front do to an abrupt change in stream gradient;