7. 
The gravitational attraction between two objects is given by the formula F= G(m_{1}m_{2}/d^{2}) where m represents the masses of the two objects, d is the distance between them and G is the gravitational constant (note: G = 6.67 x 10^{11}m^{3}kg^{1}s^{2}). (a) Calculate the gravitational force between two objects (m_{1} = 450,000 kg, m_{2} = 1,500,000 kg) that are separated by 70 meters. (b) Then determine what the force is if m_{1} is doubled and d is decreased by a factor of 1/3 (hint: calculate what to subtract first and then subtract from d; do not just multiply d by the fraction).


8. 
If the ratio of difficult physics problems to easy physics problems in a book is 4 to 3, how many easy problems are there if there are 320 problems in the book? Round your answer to the nearest whole number if necessary.

