Question

Please, I desperately need help with a Physics lesson!

Answer 1

Ok, so I’m an online student and these are questions I absolutely cannot answer! I don't have a teacher, so it would be nice if you explained each one. I’m not simply looking for answers; I need some explanation if you can. Thanks in advance!

1) Car A has twice the mass of Car B; both travel at the same speed. Compared to Car B, Car A has:

- one-fourth the energy
- twice the energy
- one-half the energy
- four times the energy
- the same the energy

2)A motor has electrical energy equivalent to 400. joules of work. It can lift a 5.0 kg mass 2.0 meters. Calculate the work done by the motor.

3) Two bricks of the same mass are each on ledges. Brick 1 is 100 feet high and Brick 2 is 300 feet high. Brick 2 has

-zero times more potential energy
-two times more potential energy
-three times more potential energy
-four times more potential energy
-nine times more potential energy

4)Cars A and B have the same mass, but Car A's speed is 15 mph, whereas Car B is moving at 60 mph. The kinetic energy of Car B is:

-1/16th times that of Car A
- 1/4 times that of Car A
-2 times that of Car A
-4 times that of Car A
-16 times that of Car A

5) A motor requires 400. joules of energy to lift a 5.0 kg mass 2.0 meters. Calculate the efficiency of this motor.

Answer 2

1) The car has kinetic energy which is given by: \[KE = \frac{ 1 }{2} m v^2\]
since the speed of the two cars are equal, the only different quantity is the mass. Thus, car A has twice the energy of car B (since it's mass is twice as big)

3) This question deals with potential energy which is given by \[PE = mgh\] when near the surface of the earth. Since their mass is equal but are at different heights, the ratio between their PE is the ration between their heights. Thus, brick 2 has three times more potential energy.

4) Same as 1, but this time their speeds differ. The ratio between their KE is the ratio between the square of their speed, and since \[\frac{ 60^2 }{ 15^2 } = 16\] the kinetic energy of car B is 16 times that of car A.

Answer 3

Thank you so much! I really appreciate your detailed response!