An LED is placed in the circuit pictured below. You would like to choose a resistor value for R2 such that the current through the diode is 20mA. If the forward bias threshold voltage for your diode is 3 and the input voltage to the circuit is 4, what should the resistance be in ohms

Visualize the problem and identify special cases first examine the problem by drawing a picture and visualizing the motion. apply newton's 2nd law, ∑f⃗ =ma⃗ , to each body in your mind. don't worry about which quantities are given. think about the forces on each body: how are these consistent with the direction of the acceleration for that body? can you think of any special cases that you can solve quickly now and use to test your understanding later? one special case in this problem is if m2=0, in which case block 1 would simply fall freely under the acceleration of gravity: a⃗ 1=−gj^.