Directions: Half page of notes, calculators permitted, no books. Show ALL work.

Question

Directions: Half page of notes, calculators permitted, no books. Show ALL work. Gravitational constant: 6.67x10 1lNm2/kg Multiple Choices (each has 6 points) 1. Who has a greater weight-to-mass ratio, a person weighing 100 lb or a person weighing 150 lb? O neither, their ratios are the same O the person weighing 100 lb the person weighing 150 lb O The question can't be answered; not enough information is given 2. Two objects attract each other gravitationally with a force of2.5x10-10 N when they are 0.25 m apart. Their total mass is 4.00 kg. Find their individual masses. O 1.84 kg, 2.16 kg O 2.84 kg, 1.16 kg O 3.94 kg, 0.06 kg O 1.94 kg, 2.06 kg O none of the above A container of water is lifted vertically 3.0 m, then returned to its original position. If the total weight is 30. N, how much work was done? 3. O No work was done. O 90 J O 45 J O 180 J 900 J A toy rocket, weighing 10 N, blasts off from ground level. At the exact top of its trajectory, its energy is 140 J. To what vertical height does it rise? 4. 01,4 m 012 m 014 m 00.12 m ?2.4 m A 1.0 kg flashlight falls to the floor. At the point during its fall when it is 0.70 m above the floor, its potential energy exactly equals its kinetic energy. How fast is it 5. 0 6.9 m/s 14 m/s 45 m/s ? 9.8 mis ? 3.7 m/s

Explanation / Answer

(1)

weight W = m*g

weight to mass , W/m = g ( gravitational constant)

for both persons the weight to mass ration is equal to g ( constant)

OPTION

neither , their ratios are same

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2)

given m1 + m2 = 4 kg

m2 = 4 - m1

gravitational force F = G*m1*m2/r^2

2.5*10^-10 = 6.67*10^-11*m1*(4-m1)/0.25^2

m1 = 3.94 kg

m2 = 0.06 kg

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3)

during lifting

work done W1 = m*g*h*cos0 = m*g*h

during returning

work done W2 = m*g*h*cos180 = -m*g*h

totla work = 0

OPTION

NO work was done

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4)

given

weight mg = 10 N

at the top ,the rocket has only potential energy

PE = m*g*h = 140

10*h = 140

h = 14 m <<<--------ANSWER

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5)

at point h = 0.7

potential energy PE = m*g*h

kinetic energy KE = (1/2)*m*v^2

given KE = PE

(1/2)*m*v^2 = m*g*h

(1/2)*v^2 = g*h

v = sqrt(2*g*h)

v = sqrt(2*9.8*0.7)

v= 3.7 m/s <<<<<------------ANSWER

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