Someone throws a 1k mass vertically on a balcony 10m above the ground at a speed of 10ms

(1) From the kinetic energy theorem: W 12mv

12×1×1J＝50J

2) Let the kinetic energy of the grapefruit be equal to one-half of the gravitational potential energy when the rising height is h, and the ground is the zero potential energy surface, then the gravitational potential energy is mgh and the kinetic energy is 1

2mgh, which is obtained from the conservation of mechanical energy: 12

mv+mgh

mgh+12mgh

i.e.: 50 mGH+1

2mgh solution: 50+10 10 10 h+1

2×10×h

Solution: h=10m

Answer: (1) This person does 50J of grapefruit

2) At 10m above the ground, the kinetic energy of the grapefruit is equal to one-half of the gravitational potential energy

（1）50J

2) 10m work: 1. Definition of work: the product of the force and the displacement acting in the direction of the force. It is a physical quantity that describes the effect of force on the accumulation of space, and it is a process quantity.

2. There are two necessary elements of work: the force acting on the object; The displacement of the object that occurs in the direction of the force.

3. The definition of work: W=Fscos, where F is the constant force, s is the displacement of the application point, and is the angle between the force and the displacement (the unit joule of work, referred to as coke, symbol J).

4. Calculation of work.

The work of constant force can be calculated according to W=FScos, and this formula is only applicable to the work done by constant force;

According to W=P·t, the average work done over a period of time is calculated;

The kinetic energy theorem is used to calculate the work of force, especially the work done by variable force;

Work can be found in turn according to the measure of energy transformation.

Methods for judging the work done by force:

Whether a force does work on an object or not, whether it does positive work or negative work, the method of judging is as follows:

1) Look at the angle between force and displacement, or between force and velocity: when it is an acute angle, the force does positive work on the object; When it is obtuse, the force does negative work on the object; When it is at a right angle, the force does no work on the object.

2) See if there is energy conversion between objects: if there is energy transformation, it must do work forcefully. This method is often used when connected objects are moving in a curvilinear motion.