An athlete is working out in the weight room. he steadily holds 50 kilograms above his head for 10 seconds. which statement is true about this situation? a. the athlete isn't doing any work because he doesn't move the weight. b. the athlete isn't doing any work because he doesn't hold the weight long enough. c. the athlete is doing work because he prevents the weight from falling downward. d. the athlete is doing work because 50 kilograms is a significant load to lift.

A. The athlete isn't doing any work because he doesn't move the weight.

Explanation:

As we know that work done is defined as the product of force and displacement of the object in the direction of the force

so here we can say

now we know that here force is applied by the athlete to hold the mass but the mass is steady at its position

The mass is not moving so we can say that

so the work done by the athlete will be zero

so correct answer is

A. The athlete isn't doing any work because he doesn't move the weight.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

the only real purpose of sputnik 1 was to beat the us into space. we were getting close to launching a useful satellite, explorer 1 - which launched on january 31, 1958. the ussr had to beat that, so they launched sputnik 1 on october 4, 19