4. A hockey puck weighs 110 g. If a puck with initial velocity of 6.0 m/s slides

Question

4. A hockey puck weighs 110 g. If a puck with initial velocity of 6.0 m/s slides for 15 m on ice before stopping, what is the magnitude of the frictional force between the puck and the ice? (Points: 6)
0.056 N
0.078 N
0.098 N
0.13 N


5. If the kinetic energy of a football player running at 8.1 m/s is 3610 J, what is the mass of that player? (Points: 6)
110 kg
125 kg
135 kg
155 kg

10. A tank 5.00 inches by 9.00 inches is filled with mercury. How deep is the tank if the total force at the bottom of the tank is 165 pounds? (The density of mercury is 0.490 lb/in3.) (Points: 6)
7.48 inches
11.27 inches
14.76 inches
15.98 inches


11. The small piston of a hydraulic press has an area of 10.0 cm2. If the applied force is 50.0 N, what is the area of the large piston so that the pressing force is 4800 N? (Points: 6)
96 cm3
480 cm3
960 cm3
4800 cm3




12. A metal block weighs 81 lb in air and 68.0 lb under water. What is the buoyant force of the water? (Points: 6)
13.0 lb
94 lb
149 lb
253 lb

Explanation / Answer

(4)accelaeration a =v^2 - u_2   / 2s

v final velocity = 6.0 m/s^2   u   = intial velocity   = 0.0 m/s^2

s = 15 m

then a   = -1.2 m/s^2

frictonal force = -F_net   = ma   = (110 *10^-3 kg * 1.2) = 0.132 N

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(5)Kinetic energy K   = (1/2)mv^2

mass m   = 2K / v^2    = 2(3610 j )/ (8.1)^2 =110 kg

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(11)F_1 /A_1   = F_2 /A_2

A_2 = F_2 *A_1 / F_1 = (10 cm^2)(4800 N) / (50 N) = 960cm^2

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(12)bouyant force = lose in weight    = W_air - W_water   = 81 N - 68 N   = 13 N

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