How do scientists look for black holes in space? Describe what a black hole looks like using one of the different ways of seeing the sky?

We put a force of 50n on an object and the acceleration is 100 m/s². what is the mass of the object?

(2) (a) you have a simple circuit that consists of only a battery (δvbat=1.5v) and two resistors with resistance r1=10ω and r2=5ω, connected in series with each other. what is the current running through the battery? (b) you re-arrange your circuit so now r2 is attached in parallel to r1 rather than in series. what is the current running through the battery? (c) you add an additional resistor r3=7ω on the same branch as r2. what is the current running through the battery? (d) what is the power dissipated in r3?

If you put a helium-filled balloon in the refrigerator, what will happen?