Unit 4

centripetal force

occurs when the direction of the velocity changes towards the center of curvature

a_c

v²/r

as velocity goes up, how are forces impacted?

F_c goes up and F_n goes down

You throw an object straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work is negative on the way up and positive on the way down because it depends on the direction of the force of gravity

Three cars are moving at the same speed and then suddenly slam on their brakes. All three of them have identical coefficients of kinetic friction. Which is the car with the most amount of work done by friction: the largest, the middle, or the smallest?

the largest car

if the force of an object is the negative direction, the work on the object must be

either positive or negative, depending on the direction of the movement

A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process?

0 Joules because there is no displacement

does a 500kg object moving at 40 m/s or a 1000kg object moving at 20 m/s have a larger kinetic energy?

they have equal kinetic energy

a truck has 4 times the mass of a car and twice the speed of it as well. describe the relationship between their kinetic energies.

the kinetic energy of the truck is twice the speed of the car because k = mv²/2

Three differently sized cars are moving at the same speed and slam on their breaks. if the tires of all three cars have identical coefficients of friction, which car travels the longest to stop, the largest, the middle, or the smallest?

they all travel the same distance in stopping

you slam on the brakes of your car and skid a certain distance on a straight-level road. If you had been traveling twice as fast, what distance would the car have skidded under the same conditions?

four times as far because velocity is squared in the kinetic energy equation

a stone is held at a certain height above the ground, and another stone four times as large is held from the same height. what is the gravitational potential energy of the second stone compared to the first stone?

four times as much

a heavy rock and a light rock are dropped from the same height and experience no significant air resistance. what is true about their speed and kinetic energy?

both rocks have the same speed when they reach the ground and when they reach the ground the heavier rock has more kinetic energy

a person stands on the side of a cliff and throws three rocks; one upwards, one downwards, and one horizontally. if the ground at the base of the cliff is level, which rock hits the ground with the greatest speed if there is no air resistance?

they all hit the ground at the same speed because of the conservation of energy