Question 1: Keeping what you leant from the passage, solve the following problem - An ice cream seller pushes a cart on a straight road. His mass is 70.0 kg, the cart’s weight is 10 kg, and the ice-cream’s weight along with dry ice is 20 kg. What will be the acceleration produced when the ice-cream exerts a backward force of 200 N on the floor? All forces opposing the motion, such as friction on the cart’s wheels and air resistance, total 20.0 N.
A. -1.5m/s2
B. 1.5m/s2
C. -1.8 m/s2
D. 1.8 m/s2
Answer Analysis
The correct answer is D.
Since they accelerate as a unit, we define the system to be the ice-cream seller, cart, ice-cream and dry ice used for storage. The seller pushes backward with a force Ffoot of 200 N. According to Newton’s third law, the floor exerts a forward reaction force Ffloor of 200 N on the system. Because all motion is horizontal, we can assume there is no net force in the vertical direction. The problem is therefore one-dimensional along the horizontal direction. As noted, f opposes the motion and is thus in the opposite direction of Ffloor. Note that we do not include the forces Fseller or Fcart because these are internal forces, and we do not include Ffoot because it acts on the floor, not on the system. No other significant forces are working on the system. If the net external force can be found from all this information, we can use Newton’s second law to find the acceleration as requested.
Newton’s second law of motion is given by:
a= F net/m total
a = Acceleration; F=Force; M=mass
The net external force on System 1 is deduced from the discussion above to be
Fnet = Ffloor − f = 200-20 = 180 N.
The mass of System is
m= (70.0+10.0+20.0) = 100 kg.
These values of Fnet and m produce an acceleration of
a = Fnet/m total
a = 180N/100kg = 1.8m/s2
Question 2: A coin is tossed straight up into the air. After it is released, it moves upward, reaches its highest point and falls back down again. What force is acting on the coin at its highest point? Air resistance can be neglected
A. Force is zero
B. Force is up and constant
C. Force is down and constant
D. Force is down and decreasing
Answer Analysis
The correct answer is C.
In the absence of air resistance, all objects fall with constant acceleration g, toward the surface of the Earth. On the surface of Earth, they are defined as g= 9.8m/s2. Using the formula F=mg we get F=mX9.8N until the object hits the ground.
Question 3: Two trucks, one of mass 1000kg and one of mass 2000kg, collide head on. The truck with more mass experiences a(n) __________ force and a(n) __________ acceleration with respect to the smaller truck
A. larger . . . smaller
B. smaller . . . larger
C. equal . . . smaller
D. equal . . . larger
Answer Analysis
The correct answer is C.
The trucks will experience the same force, due to Newtown's third law. Because the larger truck experiences the same force and has a larger mass, it will have a smaller acceleration by Newton's first law.