1. Chapter 5 Practice problems
Net Force

2. 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?

3. Sample #1
Given: m = 1500 kg a = m/s2
Unknown: Force, F

4. Sample #1
Basic equation:
F = ma

5. Sample #1
Answer: 4500 N force

6. Sample #2
Finding force when acceleration must be calculated:

7. 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 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?

8. 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

9. Sample #2
Answer: 1.1 X 107 N

10. 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

11. Sample #3 Calculating weight:
Find the weight of a 2.26 kg bag of sugar

12. Sample #3
g= 9.8 m/s2
Equation: W = mg

13. Sample #3
Answer : 22.1 N

14. 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

15. 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

16. Sample #4
Basic equation = F= ma Ff = FμFN

17. Sample #4

18. Sample #4
Because a = 0 the force you exert, FA must be equal to Ff