Classical Mechanics Answers

1) A 40.0 kg box, initially at rest, is pulled through 12.0 m along a horizontal surface. A 75.0 N pulling force is applied at 25.0° from the horizontal. If the frictional force is 14.2 N:

a. How much work was done by the applied force on the box?

b. How much work was done by the frictional force?

c. What is the net work?

d. What is the final speed of the box?

2) A machine has an output power of 13.0 kW. How long would it take for the machine to raise a 4000 kg load through a height of 2.4 m?

3) A 4.0 kg ball is swung at a constant speed in a vertical circle of radius 2.5 m. If the ball completes one revolution in 3.0 s, what is the tension in the rope at the top of the circle?

1) A 60.0-kg student runs at a constant velocity up a flight of stairs. If the vertical distance of the stairs is 3.2 m, the work done against gravity is ___x10^3 J 

Use the information below to answer the following 4 questions.

A 10.0-kg object is accelerated horizontally from rest to a velocity of 11.0 m/s in 5.00 s by a horizontal force.

2) The acceleration of the object is ___m/s²

3) The horizontal force given to the object is ___N

4) The distance travelled by the object is ___m.

5) The work done on the object is ___J.

1) A garage door opener is rated at 373 W. In 14.0 s of operation the opener can do ___x10³ J of work.

2) An automobile engine exerts a force of 595 N to propel the car at 90.0 km/h on a level road. The power output of the engine at that time is ___x10⁴ W.

Use the information below to answer the following

A traditional, double-seat chairlift can move1200 people in 1.00 hrs (with an average mass of 60.0 kg) up a ski hill. A high-speed quad chair can move 2400 people in 30.0 minutes up the hill. The upper terminal (top of the hill) is 100 m higher than the lower terminal (bottom of the hill).

4) The amount of power the double-seat chair requires just to overcome gravity is ___x10⁴ W. 

5) An electric motor has a power rating of 1.60 kW and operates at 75% efficiency. The amount of work that it can do in 1.0 hrs is ___x10⁶ J.

True or False. When non-conservative forces are present, the amount of work done increases with the length of the path.

Use the information below the answer the following 3 questions.

A 50 kg crate is being dragged across a floor by a force of 225 N at an angle of 40^o from the horizontal. The crate is dragged a distance of 5.0 m and the frictional force is 60 N.

1) The work done on the crate by the applied force is ___x10² Nm.

2) The work done on the crate by the frictional force is -___x10² Nm.

3) The net work done on the crate is ___x10² Nm.

Do not use rounded answers in subsequent calculations!

Use the information below to answer the following 2 questions.

A rubber-band slingshot is drawn back is drawn back 0.15 m with a force of 28 N and shoots a 28-g stone. Solve using energy considerations. Recall from the previous lesson that E_p = ½ kx². Since F = kx, E_p = ½ Fx.

1)The initial speed of the stone if the rubber band is released is___m/s

2) The maximum height of the stone if it is shot straight up is ___m

Use the information below to answer the following 2 questions.

A 0.80-kg coconut is growing 10 m above the ground in its palm tree. The tree is just at the edge of a cliff that is 15 m tall.

1) The maximum speed of the coconut if it fell to the ground beneath the tree is ___m/s.

2) The maximum speed of the coconut if it fell from the tree to the bottom of the cliff is ___m/s

A rocket of mass 1000kg moves vertically upward with an acceleration of 4.0m/s² . What is the total force generated by it engines? (g=9.8m/s² .)

A stone of mass 1kg is thrown vertically downward from a rope at a velocity of 2m/s. At the moment it hits the soils, the stone has a kinetic energy of 200J. What is the height from which the stone is thrown?

Sketch a graph showing the logarithm of the force between two charges(on the y-axis) against the logarithm of the distances separating the two charges.