Cracking the SAT Physics Subject Test

AN OVERALL STRATEGY The previous problems were simple force problems. For other, more complicated problems involving multiple fo ...

Third, combine the force vectors and determine the net force: This will require you to use the Superposition Principle (for vect ...

A crate of mass 20 kg is sliding across a wooden floor. The coefficient of kinetic friction between the crate and the floor is 0 ...

The normal force on the object balances the object’s weight, so FN = mg = (20 kg)(10 m/s^2 ) = 200 N. Therefore, Ff (kinetic) ...

A crate of mass 100 kg rests on the floor. The coefficient of static friction is 0.4. If a force of 250 N (parallel to the floo ...

PULLEYS Pulleys are devices that change the direction of the tension force in the cords that slide over them. For the purposes o ...

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Pulleys can also be used to decrease the force necessary to lift an object. For example, consider a pulley system like the one a ...

with a constant velocity our net force should be zero since there is no acceleration. The total of all tension forces pulling up ...

In the previous diagram, assume that the tabletop is frictionless. Determine the acceleration of the blocks once they’re releas ...

To get the acceleration of each one, we use Newton’s second law, Fnet = ma. Notice that there are two unknowns, FT and a, but we ...

A quicker way of solving for the acceleration is to treat the entire system (blocks plus string) as one object. Since we are onl ...

inclusion of friction, Ff , that acts on the block on the table. As before, we have two equations that contain two unknowns (a a ...

Mg − FT = Ma (2) We add the equations (thereby eliminating FT) and solve for a. Notice that, by definition, Ff =μFN and from the ...

what’s being accelerated. When doing your net force calculations, bear in mind that the system of objects accelerates at the sam ...

INCLINED PLANES An inclined plane is basically a ramp. If an object of mass, m, is on the ramp, then the force of gravity on the ...

the component of gravity down the inclined plane by thinking “sine” equals “sliding.” Here’s How to Crack It Let m be the mass o ...

The force of friction, Ff, that acts up the ramp (opposite to the direction in which the block slides) has magnitude Ff = μFN. B ...

Remember that frictional force is calculated by multiplying the coefficient of friction, μ, by the normal force, N, not the weig ...

Chapter 3 Comprehensive Drill See Chapter 17 for solutions. A person standing on a horizontal floor feels two forces: the downw ...