Cracking the SAT Physics Subject Test

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Once again, Situation 1 yields the fastest door-shutting results, followed by Situation 2. (In Situation 3, the door is being pu ...

There’s no special name for this unit; it’s just called a newton-meter. Because it is not in newtons, torque is NOT a force, but ...

(or moment arm) of the force F relative to the pivot and is symbolized by l. The torque of F is defined as the product τ = lF Th ...

A student pulls down with a force of 40 N on a rope that winds around a pulley of radius 5 cm. What’s the torque of this force ...

Therefore, the torque produced by this tension force is τ = rFT = (0.05 m)(40 N) = 2 N·m The cylinder below is free to rotate a ...

Here’s How to Crack It Each of the two forces produces a torque, but these torques oppose each other. The torque of F 1 is count ...

τnet = Σ τ = τ 1 + τ 2 = (+12 N·m) + (−6.4 N·m) = +5.6 N·m ...

EQUILIBRIUM An object is said to be in translational equilibrium if the sum of the forces acting on it is zero—that is, if Fnet ...

Here’s How to Crack It Let T 1 be the tension in the left-hand rope and let T 2 be the tension in the right-hand rope. We’ll wri ...

Look at the point where the two ropes meet. Since the system is in static equilibrium, the net force on this point must be zero. ...

This gives us the tension in each of the ropes noted in the figure. The figure below shows a homogeneous bar of mass M and leng ...

Look at the point where the bar is attached to the wall. Since the system is in static equilibrium, the net torque about this po ...

wall force. ...

ANGULAR MOMENTUM So far we’ve developed rotational analogs for displacement, velocity, acceleration, and force. We will finish b ...

Then, by Newton’s second law If we multiply both sides of this equation by r and notice that rF = τ, we get Therefore, to form t ...

If r is the vector from the reference point to the mass, then the angular momentum is L = rmv⊥ = rmv sin θ where v⊥ is the compo ...

Recall that objects naturally resist changes to their velocity. The greater the inertia (partially measured by mass), the harder ...

CONSERVATION OF ANGULAR MOMENTUM Newton’s second law says that so if Fnet = 0, then p is constant. This is conservation of linea ...

ROTATIONAL KINEMATICS If we mark several dots along a radius on a disk and call this radius the reference line, and the disk rot ...