How long must a motorcyclist accelerate in order to reach a speed of 72 km / h from a state of rest, with a traction

How long must a motorcyclist accelerate in order to reach a speed of 72 km / h from a state of rest, with a traction force of 1200 N and a friction force of 200 N? The mass of a motorcyclist with a driver is 200 kg.

V0 = 0 m / s.
V = 72 km / h = 20 m / s.
F = 1200 N.
Ftr = 200 N.
m = 200 kg.
t -?
The motorcyclist moves horizontally under the action of 2 forces: traction force F, which is directed in the direction of movement, friction force Ffr, directed in the opposite direction of movement.
Let’s write 2 Newton’s law: m * a = F – Ftr.
The acceleration of the body a is determined by the formula: a = (V – V0) / t. Since V0 = 0 m / s, the formula will take the form: a = V / t.
m * V / t = F – Ftr.
t = m * V / (F – Ftr).
t = 200 kg * 20 m / s / (1200 N – 200 N) = 4 s.
Answer: the motorcyclist’s acceleration time is t = 4 s.




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