Zubrzycki: Dynamics 5

Practice With Newton’s Second Law

  1. (Multiple choice) Two small balls of the same material, one of mass m and the other of mass 2m, are dropped simultaneously from the Leaning Tower of Pisa. Earth exerts a bigger force:

a)On the 2m ball.

b)On the m ball.

c)Earth exerts same force on both balls because they fall with the same acceleration.

  1. During a football workout, a football linemen is pushing the coach on the sled. The combined mass of the sled and the coach is 300 kg. The sled accelerates at a rate of 0.580 m/s2.

a)Draw a force diagram. Remember to label each force.

b)Determine the force exerted on the sled by the linemen.

  1. You pull a 20-kg sled, exerting a horizontal force of 30 N on it for 10 seconds.

a)What is the acceleration of the sled?

b)What is the speed of the sled after 3 seconds?

  1. A 750 N upward force is being exerted by a cable on a 500 kg downward-moving freight elevator.

a)Draw a force diagram for this situation. Remember to label each force.

b)Determine the acceleration of the elevator.

c)If you need to, fix your force diagram to correspond to the values that you determined for the two interactions.

  1. In a grocery store, you push a 14.5 kg shopping cart. It is initially rolling at a constant speed of 2.0 m/s. You push on it in the direction opposite to its motion exerting a force of 12.0 N.

a)Draw a force diagram and a motion diagram for the cart when you start pushing in the direction opposite to its motion.

b)Assuming you push the cart exerting constant force for a while, how far will it travel in 3 seconds? (Ignore friction for all parts of this problem.)

  1. Mr. Z is back on his roller blades again now carrying 10 physics books and Kim is pushing him. The combined mass of Mr. Z and physics books is 86 kg.

a)Draw a force diagram. Remember to label each force.

b)If Kim is pushing Mr. Z exerting a force of 45 N, what is the acceleration of Mr. Z?

  1. Equation Jeopardy Describe in words a problem for which the following equation is a solution and draw a force diagram that is consistent with the equation (specify the direction of the axis):

-196 N + F P on O = (20 kg)(-2.0 m/s2)

  1. Spider-Man holds the bottom of an elevator with one hand. With his other hand, he holds a spider cord attached to a 50 kg box of explosives at the bottom of the cord. Determine the force that the cord exerts on the box if:

a)The elevator is at rest

b)The elevator accelerates up at 2.0 m/s2

c)The elevator moving upward with some initial speed decreases it’s speed at a rate of 2.0 m/s2

d)The elevator falls freely

  1. A 2.1 x 104 kg F-18 Super Hornet jet airplane goes from zero to 265 km/h in 90 m during takeoff from the flight deck of an aircraft carrier. What physical quantities can you determine using this information? Make a list and determine the values of three of them.
  1. A 60 kg astronaut sits on a bathroom scale in a rocket that is taking off vertically with an acceleration of 3 g. What does the scale read?
  1. An 80 kg fireman slides 5.0 m down a fire pole. He holds the pole, which exerts a 500 N steady resistive force on the fireman. At the bottom he slows to a stop in 0.40 m by bending his knees. What can you determine using this information? Determine everything you can.