Question

# 21) A person carries a 25.0-N rock through the path shown in the figure, starting at...

21) A person carries a 25.0-N rock through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 1.50 min. How much work did gravity do on the rock between A and B?

A) 625 J

B) 20.0 J

C) 275 J

D) 75 J

E) 0 J

22) A person carries a 2.00-N pebble through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 6.75 min. How much work did gravity do on the rock between A and B?

A) 30.0 J

B) -30.0 J

C) -56.0 J

D) 56.0 J

E) -36.0 J

23) An object hits a wall and bounces back with half of its original speed.  What is the ratio of the final kinetic energy to the initial kinetic energy of the object?

A) 1/2

B) 1/4

C) 1/8

D) 1/16

24) When a car of mass  accelerates from 10.0 m/s to some final speed, 4.00 ×105 J of work are done. Find this final speed.

A) 28.0 m/s

B) 22.4 m/s

C) 25.2 m/s

D) 30.8 m/s

25) A 100-N force has a horizontal component of 80 N and a vertical component of 60 N.  The force is applied to a cart on a level frictionless floor.  The cart starts from rest and moves 2.0 m horizontally along the floor due to this force.  What is the cart's final kinetic energy?

A) 200 J

B) 160 J

C) 120 J

D) zero

26) A sled having a certain initial speed on a horizontal surface comes to rest after traveling 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what was the initial speed of the object?

A) 9.8 m/s

B) 6.3 m/s

C) 3.6 m/s

D) 7.2 m/s

E) 8.9 m/s

27) A stone is moving on a rough level surface. It has 24 J of kinetic energy, and the friction force on it is a constant 0.50 N.  What is the maximum distance it can slide?

A) 2.0 m

B) 12 m

C) 24 m

D) 48 m

28) In a ballistics test, a 28-g bullet pierces a sand bag that is  thick. If the initial bullet velocity was  and it emerged from the sandbag moving at  what was the magnitude of the friction force (assuming it to be constant) that the bullet experienced while it traveled through the bag?

A) 130 N

B) 38 N

C) 13 N

D) 1.3 N

29) You do 116 J of work while pulling your sister back on a fritctionless swing, whose chain is  long, until the swing makes an angle of 32.0° with the vertical. What is your sister's mass?

A) 15.3 kg

B) 13.0 kg

C) 17.6 kg

D) 19.0 kg

30) An ideal spring stretches by 21.0 cm when a 135-N object is hung from it. If instead you hang a fish from this spring, what is the weight of a fish that would stretch the spring by

A) 199 N

B) 91 N

C) 145 N

D) 279 N

31) If 4.0 J of work are performed in stretching an ideal spring with a spring constant (force constant) of 2500 N/m, by what distance is the spring stretched?

A) 3.2 cm

B) 3.2 m

C) 0.3 cm

D) 5.7 m

E) 5.7 cm

32) How much work is required to stretch an ideal spring of spring constant (force constant) 40 N/m from x= 0.20 m to x= 0.25 m if the unstretched position is at x= 0.00 m?

A) 0.45 J

B) 0.80 J

C) 1.3 J

D) 0.050 J

33) A rock falls from a vertical cliff that is 4.0 m tall and experiences no significant air resistance as it falls. At what speed will its gravitational potential energy (relative to the base of the cliff) be equal to its kinetic energy?

A) 3.1 m/s

B) 4.4 m/s

C) 6.3 m/s

D) 8.9 m/s

E) 13 m/s

34) A prankster drops a water balloon from the top of a building. If the balloon is traveling at 29.1 m/s when it strikes a window ledge that is 1.5 m above the ground, how tall is the building? Neglect air resistance.

A) 45 m

B) 43 m

C) 46 m

D) 47 m

35) The figure shows a famous roller coaster ride. You can ignore friction. If the roller coaster leaves point Q from rest, what is its speed at the top of the 25-m peak (point S)?

A) 10 m/s

B) 22 m/s

C) 44 m/s

D) 62 m/s

E) 120 m/s

36) Assuming negligible friction, what spring constant (force constant) would be needed by the spring in a "B-B gun" to fire a 10-g pellet to a height of 100 m if the spring is initially compressed by 0.10 m?

A) 20 N/cm

B) 20 N/m

C) 200 N/m

D) 2000 N/cm

E) 0.0020 N/m

37) A toy rocket that weighs 10 N blasts straight up from ground level with an initial kinetic energy of 40 J.  At the exact top of its trajectory, its total mechanical energy is 140 J.  To what vertical height above the ground does it rise, assuming no air resistance?

A) 1.0 m

B) 10 m

C) 14 m

D) 24 m

38) In the figure, a ball hangs by a very light string. What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0 m above the bottom of the swing?

A) 2.2 m/s

B) 3.1 m/s

C) 4.4 m/s

D) 4.9 m/s

#### Homework Answers

Answer #1

for 21 and 22 figure is required.

23)

kinetic energy = 1/2 mv^2

thus the ratio would be

(0.5)(m)(0.5v)^2/ ( 0.5)(m)(v)^2

0.5 for one half the origional velocity, the direction doesn'tmatter since the v is squared.

the mass and one half of the equation cancels, as well as thearbitrary value of v,

thus we have

0.5^2/1^2 = 1/4

thus it has 1/4 as much kinetic energy

24)

change in kinetic energy = work done

In this problem mass is required

25)

ΔK = W = Fxx = 80(2) = 160 Joules

26)

acceleration of the sled, a = -g*mue_k

= -9.8*0.2

= -1.96 m/s^2

let u is the initial speed and v is the final speed.

Apply, v^2 - u^2 = 2*a*d

0^2 - u^2 = 2*(-1.96)*10

u = sqrt(2*1.96*10)

u = 6.26 m/s

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