AP Review Work and Energy

A force F at an angle θ above the horizontal is used to pull a heavy suitcase of weight mg a distance d along a level floor at constant velocity. The coefficient of friction between the floor and the suitcase is µ. The work done by the frictional force is:

• –Fd cos θ

• – µ Fd cos θ

• - µmgd

• -µ mgd cos θ

A softball player catches a ball of mass m, which is moving towards her with horizontal speed V. While bringing the ball to rest, her hand moved back a distance d. Assuming constant deceleration, the horizontal force exerted on the ball by the hand is

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  $\frac{mv^2}{2d}$

• $\frac{mv^2}{d}$

• $\frac{2mv}{d}$

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  $\frac{mv}{d}$

A car of mass m slides across a patch of ice at a speed v with its brakes locked. It the hits dry pavement and skids to a stop in a distance d. The coefficient of kinetic friction between the tires and the dry road is µ.

• 0.5 d

• d

• 1.41 d

• 2 d

A car of mass m slides across a patch of ice at a speed v with its brakes locked. It the hits dry pavement and skids to a stop in a distance d. If the car has a speed of 2v, it would have skidded a distance of

• 4 d

• d

• 1.41 d

• 2 d

A football is kicked off the ground a distance of 50 yards downfield. Neglecting air resistance, which of the following statements would be INCORRECT when the football reaches the highest point?

• the ball will have been in the air one-half of its total flight time

• the vertical component of the velocity is equal to zero

• the ball’s horizontal velocity is the same as when it left the kickers foot

• all of the balls original kinetic energy has been changed into potential energy

A fan blows the air and gives it kinetic energy. An hour after the fan has been turned off, what has happened to the kinetic energy of the air?

• it disappears

• it turns into potential energy

• it turns into thermal energy

• it turns into sound energy

A rock is dropped from the top of a tall tower. Half a second later another rock, twice as massive as the first, is dropped. Ignoring air resistance,

• they strike the ground with the same kinetic energy.

• they strike the ground more than half a second apart.

• the acceleration is greater for the more massive rock.

• the distance between the rocks increases while both are falling

From the top of a high cliff, a ball is thrown horizontally with initial speed vo. Which of the following graphs best represents the ball's kinetic energy K as a function of time t ?

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A rock of mass m is thrown horizontally off a building from a height h, as shown above.  The speed of the rock as it leaves the thrower’s hand at the edge of the building is v0. What is the kinetic energy of the rock just before it hits the ground?

•  $mgh$  

•  $\frac{1}{2}mv_0^2$  

•  $\frac{1}{2}mv_0^2\ -\ mgh$  

•  $\frac{1}{2}mv_0^2\ +\ mgh$  

The following graphs, all drawn to the same scale, represent the net force F as a function of displacement x for an object that moves along a straight line. Which graph represents the force that will cause the greatest change in the kinetic energy of the object from x = 0 to x = x₁?

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