The picture below shows a toy car in the process of rolling down a ramp. At point X, the kinetic energy is 50 Joules (J), and the potential energy is 30 J.

What is the total energy in the system once the car reaches the bottom of the ramp?
A
20 J, because the energy in the system cannot change form but can be created and destroyed

B
80 J, because the energy in the system can change form but cannot be created or destroyed

C
30 J, because the potential energy is the only energy at the bottom of the ramp

D
50 J, because the kinetic energy is the only energy at the bottom of the ramp

B 80 J, because the energy in the system can change form but cannot be created or destroyed

Explanation:

According to the law of conservation of energy, the total energy stays the same.  The car starts with a total of 80 J of energy, so it must also end with a total of 80 J of energy.

b.a device that inputs heat into a cool object

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west