PH2530 Homework Assignment 2.1

Exercises

8. When your car moves along the highway at a constant velocity, the net force on it is zero. Why,

then, do you continue running your engine?

Net force being zero is not the same as not having force act upon it. Drag and Friction are constant on

moving objects such as cars, so the engine is needed to generate force through the wheels. If the engine

was stopped then the counterforce would no longer be present and drag would eventually stop the car.

17. You hold an apple over your dead.

a. Identify all the forces acting on the apple and their reaction forces.

Two pairs of forces act, which are, the earth’s pull on the apple and the apples pull on

the earth. Then the other force pairs are your hand pushing the apple up and the apple

pushing your hand down.

b. When you drop the apple, identify all the forces acting on it as it falls and the corresponding

reaction forces.

The forces in this scenario are as fallows, the earths pull on the apple and the apples pull

on the earth, then when air is configured then the apple pushing the air downward and also the

air pushing the apple upward as well.

25. Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that

joints them is released. How fast does the heavier cart roll compared with the lighter cart?

The acceleration of the larger cart will be one half the acceleration of the smaller cart because of

Newtons 2nd law, which states F=m*a, so for this instances the formula will be used as a=F/m.

PH2530 Homework Assignment 2.1

33. Why is it that a car that falls from the top of a 50-story building will hit a safety net below no

faster than if it fell from the twentieth story?

The reason that the car does not go faster from the 20th floor to the 50th floor is because terminal

velocity has already been met within the shorter distance, so there for the car will not fall faster than its

terminal velocity.

43. A stone is shown at rest on the ground.

a. The vector shows the weight of the stone. Complete the vector diagram showing another

vector that result in zero net force on the stone.

The vector pointing down is the weight from the stone on the Earth. To make the net force zero,

you need to have an equally opposite force exerting itself on the stone, say the ground pushing its own

force against the stone, the two forces would equally cancel each other out resulting in a net force of

zero.

b. What is the conventional name of the vector you have drawn?

The conventional name that the vector represents is normal force, also called supporting force.

PH2530 Homework Assignment 2.1

Problems

12. Forces of 3 N and 4 N act at right angles on a block of mass 5 Kg. Show that the resulting

acceleration is 1 m/s².

R² = 3² + 4²

R² = 9 + 16

R² = √25

R = 5 N

F = m*a

5 N = 5 Kg/5*a

5 N/5 = 5 Kg/5*a

A = 1 m/s²

Define angular speed (rotational speed) and tangential speed, and specify units for each.

Angular speed is radians/second (rad/s). There are 2π radians in just 1 revolution.

Tangential speed is the top speed which is measured in meters/second (m/s). To find the

tangential speed, the equation rad/s * radius.