Brake Force
Consider a braking system with a 10 m long brake arm and a rotational speed of 25 rev/s. If the total brake power is 50 kW, what is the applied force (N) at the end of the brake arm?
Expand Hint
Brake Power:
$$$\dot{W}_b=2\pi \tau \upsilon =2\pi FR\upsilon $$$
where
$$\tau$$
is torque,
$$\upsilon $$
is rotational speed,
$$F$$
is the force at the end of the brake arm, and
$$R$$
is the brake arm’s length.
Hint 2
No conversion is needed for rotational speed since the problem statement specifies rev/s.
Brake Power:
$$$\dot{W}_b=2\pi \tau \upsilon =2\pi FR\upsilon $$$
where
$$\tau$$
is torque in
$$N \cdot m$$
,
$$\upsilon $$
is rotational speed in
$$rev/sec$$
,
$$F$$
is the force at the end of the brake arm, and
$$R$$
is the brake arm’s length. Thus,
$$$F=\frac{\dot{W}_b}{2\pi R\upsilon }=\frac{50,000W}{2\pi (10m)(25rev/s)}$$$
$$$=\frac{50,000kg\cdot m^2}{2\pi (10m)s^3(25\frac{rev}{s})}=\frac{50,000kg\cdot m}{1,570s^2}=31.8\:N$$$
31.8 N
Time Analysis
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