# Physics exercises

11 QUESTIONS TOTAL

1. In exploring Newton’s laws, it is important to keep in mind all the forces that

are at work in a given system and what their net effect is on a body. Suppose you simultaneously drop a hammer and a feather from the same height on the surface of the earth. Which will reach the ground first? Suppose you then do the same experiment on the surface of the moon. Does anything change? If so, what? Explain all your answers using what you have learned about Newton’s laws of motion. (There are some great video clips of this actual experiment online.) (at least 100 words response on this question)

ONE STEP CALCULATIONS

Conversion factors: 1kg weighs 10 N at Earth’s surface: 1 N = 0.22 LB

Weight = mg

3. An apple weighs about 1 N. What is its mass in kilograms? What is its weight in pounds?

Acceleration: a= Fnet

M

6.  a) Calculate the acceleration of a 2 kg block on a horizontal friction-free air table when you exert a horizontal net force of 20 N.

b) What acceleration occurs if the friction force is 4 N?

Force: F=ma

8. Calculate the horizontal force that must be applied to produce an acceleration of 1.8 g for a 1.2 kg puck on a horizontal friction free air table.

EXERCISES

5. Before the time of Galileo and Newton, it was thought by many learned scholars that a stone dropped from the top of a tall mast on a moving ship would fall vertically and hit the deck behind the mast by a distance equal to how far the ship had moved forward while the stone was falling. In light of your understanding of Newton’s laws, what do you think about this idea?

11. A common saying goes, “Its not the fall that hurts you: it’s the sudden stop.” Translate this into Newton’s laws of motion.

13. If you drop an object, its acceleration toward the ground is 10 m/s square. If you throw it down instead, would its acceleration after throwing be greater than 10 m/s sq? Ignore air resistance. Why or why not?

a. Identify all the forces acting on the apple and their reaction forces.

b. When you drop the apple, identify all the forces acting on it as it falls and the              corresponding reaction forces.

27. If a Mack truck and motorcycle have a head-on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? Explain your answers.

34. Free fall is motion in which gravity is the only force acting.

a. Is a skydiver who has reached terminal speed in free fall?

b. Is a satellite circling Earth above the atmosphere in free fall?

39. Which is more likely to break, the ropes supporting a hammock stretched tightly between a pair of trees or one that sags more when you sit on it? Defend your answer.