A man is lifting a piano that weighs 800 N through a distance of 10 meters using a pulley system. The man pulls the rope a total distance of 100m. What force does the man need to apply to the rope?

The force the man applied is 80 N

Explanation:

weight of the load, L = 800 N

distance traveled by the load, a = 10 m

distance traveled by the effort, b = 100 m

Output work = load x distance moved by the load

Output work = 800 x 10 = 8000 J

Input work = Effort x distance moved by effort

Input work = Effort x 100 m

Assuming an ideal machine; no friction effect, the input work will be equal to output work.

Effort x 100 m = 8000 J

Effort = 8000 / 100

Effort = 80 N

Therefore, the force the man applied is 80 N

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.

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.