Please show your work

1. A woman standing before a cliff claps her hands, and 2.8 s later she hears the echo. How far away is the cliff? The speed of sound in air at ordinary temperatures is 343 m/s. Please include two decimals.
2. A car whose acceleration is constant reaches a speed of 80 km/hr in 20 s starting from rest. How much moretime is required for it to reach a speed of 130 km/hr?
3. A car is moving at 10 m/s when it begins to be accelerated at 2.5 m/s^2.
   1. How long does the car take to reach a speed of 25 m/s?
   2. How far does it go during this period?
4. How fast must a ball be thrown upward to reach a height of 12m? [fast] m/s
5. A force of 20 N gives an object an acceleration of 5 m/s^2.
   1. What force would be needed to give the same object an acceleration of 1 m/s²?
   2. What force would be needed to give it an acceleration of 10 m/S²?
6. The greatest force a level road can exert on the tires of a certain 2000-kg car is 4 kN. What is the highest speed the car can round a curve of radius 200 m without skidding?
7. If the moon were half as far from the earth as it is today, how would the gravitational force it exerts on the earth compare with the force it exerts today? ___ times what it is today
8. Is the sun's gravitational pull on the earth the same at all seasons of the year? Choose one
   1. Yes, because the earth's orbit is completely circular.
   2. Yes, because the earth and the sun vary in their distance during the year.
   3. No, because the earth's orbit is circular.
   4. No, because the earth and the sun vary in their distance during the year.
9. A bull and a cow elephant, each of mass 2000 kg, attract each other gravitationally with a force of 2x10^-5 N. How far apart are they, in m?