Chapter 5 Practice problems
Net Force
Sample #1
• Using Newton’s Second Law to find the net
force on an accelerating object:
• …. What net force is required to accelerate a
1500 kg race car act at +3.00m/s2?
Sample #1
• Given: m = 1500 kg a =+ 3.00 m/s2
• Unknown: Force, F
Sample #1
• Basic equation:
• F = ma
Sample #1
• Answer: 4500 N force
Sample #2
• Finding force when acceleration must be
calculated:
Sample #2
• An artillery shell has a mass of 55 kg. The
shell is fired from a gun leaving the barrel with
a velocity of + 770 m/s. The gun barrel is 1.5
m long. Assume that the force, and thus the
acceleration is constant while in gun barrel.
What is the force on the shell while it is in the
gun barrel?
Sample #2
•
•
•
•
•
Given: M = 55 kg vf = + 770 m/s vi = 0 m/s
D = +1.5 m
Unknown: force, F
Basic equations: F = ma
Vf2 =vi2 + 2ad
Sample #2
• Answer: 1.1 X 107 N
Sample # 2
• Solution: =
• A = (+770m/s2) - 0
•
2(1.5 m)
• a = +2.0 X 105 m/s2 ( in the direction of the
velocity)
• F = 55 kg +2.0 X 105 m/s2
Sample #3
• Calculating weight:
• Find the weight of a 2.26 kg bag of sugar
Sample #3
• g= 9.8 m/s2
• Equation: W = mg
Sample #3
• Answer : 22.1 N
Sample #4
• Sliding friction:
• A smooth wooden block is placed on a smooth
wooden tabletop. You find that you must
exert a force of 14.0 N to keep the 40.0 N
block moving at a constant velocity
Sample #4
• A. What is the coefficient of friction for the
block and table?
• Given: FA = 14 N W = 40 N a = 0
• Unknown : Coefficient of friction = μ
Sample #4
• Basic equation = F= ma Ff = FμFN
Sample #4
Sample #4
• Because a = 0 the force you exert, FA must be
equal to Ff