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.

like poles repel so keep pushing north to north and repels funny to see this