مراجعة اسئلة هيكل امتحان الفيزياء الصف 11 متقدم الفصل الثاني

مراجعة اسئلة هيكل امتحان الفيزياء الصف 11 متقدم الفصل الثاني

6.1 Potential Energy

Chapter 5 examined in detail the relationship between kinetic energy and work. and one of the main points was that work and kinetic energy can be converted into one another. Now. this section introduces another kind of energy. called potential energy

Potential energy, U. is the energy stored in the configuration of a system of objects that exert forces on one another For example. we have seen that work is done by an external force in lifting a load against the force of gravity, and this work is given by W rngh, where m is the mass of the load and h =  yo is the height to which the load is lifted above its initial pc»sition. (In this chapter, we will assunue the y-axis points upward unlews specified differently.) This lifting can be accomplished without changing the kinetic energy. as in the case of a weightlifter who lifts a mass above his head and holds it there. -were is energy stored in holding the mass above the head. If the veight- lifter lets go of the mass, this energy can be converted back into kinetic energy as the mass accelerates and falls to the ground. We can express the gravitational B.tential energy as The change in the gravitational potential energy of the mass is then

(Equation 6.1 is valid only near the surface Of the Earth, where F = mg. and in the limit thar Earth is infinitely massive relative to Che object. VVe will encounter a more general expression for U in Chapter 12.) In Chapter S, we found that the work done by the gravitational force on an object that is lifted through a height he is —mgh From this, we see that the work done by the gravitational force and the gravitational potential energy for an object lifted from rest to a height h are related by

Concept Check 6 3

A spring with spring constant  is oriented vertically and compressed downward a distance x from its equilibrium position. An object of mass m is placed on the upper end of the spring, and the spring is released. The object rises a distance h (with h>x) above the equilibrium position of the spring. If the spring is then compressed downward by the same distance x and an object of mass 3m is placed on it, how high will the object rise when the spring is released

Concept Check 6 4

A ball of mass m is thrown vertically into the air with an initial speed v. Which of the following equations correctly describes the maximum height, h, of the ball

.   For an object sliding on the ground, the friction force

a) always acts in the same direction as the displacement

b) always acts in a direction perpendicular to the displacement

c) always acts in a direction opposite to the displacement

d) acts either in the sarne direction as the displacement or in the direction opposite to the displacenwnt depending on the value of the  of kinetic frÉtioru

 Some forces in nature vary With the inverse of the distance qluared between two otcts. For a force like this. how does the potential energy vary With the distance between the two objects

a) The Bitenual energy varies with the distance

b) The potential energy varies with the distance 41ared

c) energy varies with the inverse of the distance

d) The potential energy vanes With the inverse of distance squared

e) The potential energy does not opend on the distance

 The value of the momentum for a system is the same at a later time as at an earlier time if there are no

a) collisions between particles within the system

b) inelastic collisions between particles within the system

c) changes of momentum of individual particles within the system

d) internal forces acting between particles within the system

e) external forces acting on particles of the system

 Which of the following is a correct unit of power

a) kg rn/s2    d) m/s2

While a boat is being towed at a speed of 12.0 m/s. the tension in the towline is 6.00 kN. What is the power supplied to the boat through the towline,

 An arrow is placed on a bow. the bowstring is pulled back. and the arrow is shot straight up into the air. the arrow then comes back down and sticks into the ground Describe all 01 the changes in work and energy that occur

 Two identical billiard balls start at the same height and the same tirne and roll along different tracks. as in the figure

a) Which ball has the highest speed at the end

b) Which one will get to the end fire End

 A spring has a spring constant of 80. N/rn How much potential energy does it store when stretched by 10

 figure shows of pcssible nunentum vectors before and after a collism with external f«ces actirv Which is could actually occur Before

 Average Force on a Golf Ball

EXAMPLE

A driver is a golf club used to hit a golf ball a long distance. The head of a driver typically has a mass 200. g. A skilled golfer can give the club head a of around 400 Ws

mass of a golf ball is 450 g. •Ihe ball stays in contact with face of the driver for 0.500 rm

PROBLEM

What is the average force exerted on the golf ball by the driven

SOLUTION

The golf ball is initially at rest. Because the driver head and the ball are in contact for only a short time. we can consider the collision between them to be an elastic collision

We can use equation 7.18 to calculate the speed of the golf ball, after the collision with the driver head

where mi is the of the golf ball is the mass of the driver head. and is speed of the driver head lhe speed the golf ball leaving face of the driver head in this case is 2(O.200 kg)

Note that if the driver trad were much more massive than the golf ball. the golf ball would attain twice the driver head However, in that case. the would have a diffi- cult time the club a substantial speed ncxnenturn change the golf ball is The impulse is then

where F is the average force exerted by the driver head and At is the time that the driver head and golf ball are in contact- The average force is then

. the driver exerts a very large force the golf ball -nus force cornprses the golf ball significantly. as in the video sequence in 72 rwte that the driver not propel ball in horizontal direction and imparts spin to the ball. an accurate description of striking a golf ball with a driver requires a rmre detailed analysis