Physics principles and equations
Newton’s second law
ȈF = ma
The magnitude of the force of kinetic friction is found by
fk =μkFN
Step-by-step solution
We begin by determining the net horizontal force on the block.
Now we substitute the net force just found into Newton’s second law. This allows us to solve for the tension force.
Step Reason
1. ȈF = T + (–fk) net horizontal force
2. fk = μkFN equation for kinetic friction
3. ȈF = T – μkFN substitute equation 2 into 1
4. ȈF = T – μkmg enter value of FN
Step Reason
5. ȈF = ma Newton's second law
6. T – μkmg = ma substitute equation 4 into 5
7. T = μkmg + ma solve for tension
8. T = (0.200)(1.60 kg)(9.80 m/s^2 ) + (1.60 kg)(2.20 m/s^2 ) enter values
9. T = 6.66 N evaluate
5.21 - Sample problem: a force at an angle
Above, you see a bat hitting a ball at an angle. You are asked to find the net force and the acceleration of the ball along the x and y axes.
Draw a free-body diagram
The forces on the ball are its weight down and the force of the bat at the angle ș to the x axis.