Question

friction
up until this point, its been convenient to ignore one of the most useful
most troublesome forces in everyday life... a force that has tremendous
plication in transportation, machinery, and all parts of mechanics, yet pe
spend tremendous amounts of effort and money each day fighting it.
force, friction, is a force that opposes motion.
4.24 q: a projectile launched at an angle of 45° above the horizontal t
els through the air. compared to the projectiles theoretical
with no air friction, the actual trajectory of the projectile wit
friction is
(a) lower and shorter
(b) lower and longer
(c) higher and shorter
(d) higher and longer
4.25 q: a box is pushed toward the right across a classroom floor. the
force of friction on the box is directed toward the
(a) left
(b) right
(c) ceiling
(d) floor
4.28 q: the diagram below shows a 4.0 - kilogram object accelerating
10 meters per second² on a rough horizontal surface.
acceleration = 10. m/s²
frictional
force = f₁
m = 4.0 kg
applied
force = 50. n
(not drawn to scale)
what is the magnitude of the frictional force f, acting on t
ject?
(a) 5.0 n
(b) 10 n
(c) 20 n
(d) 40 n

Explanation:

Step1: Apply Newton's second law

Newton's second law is \(F_{net}=ma\). The net force \(F_{net}\) is the applied force \(F_{applied}\) minus the frictional force \(F_{f}\), so \(F_{net}=F_{applied}-F_{f}\).

Step2: Substitute values into the formula

We know \(m = 4.0\space kg\), \(a=10\space m/s^{2}\), and \(F_{applied}=50\space N\). Substituting into \(F_{applied}-F_{f}=ma\), we get \(50 - F_{f}=4\times10\).

Step3: Solve for \(F_{f}\)

First, calculate \(4\times10 = 40\). Then, rewrite the equation as \(F_{f}=50 - 40\).

Answer:

B. \(10\space N\)