Question

An object with cross section A is shot horizontally across frictionless ice. Its initial velocity is v0x at t0=0s. Air resistance is not negligible.

A 1.8 m wide, 1.5 m high, 1700 kg car with a drag coefficient of 0.35 hits a very slick patch of ice while going 24 m/s . Air resistance is not negligible. If friction is neglected, how long will it take until the car's speed drops to 11 m/s ?

To 5.0 m/s ?

Answer 1

From Newton's second law ma The drag force is (0.41 (1.225)A(v(t 4 Consider the negative sign for drag force as it acts opposite to the net force and equal the drag force tot net force 4m dt 4m (t)dt (v(r) 4m v(t) m To x 4m The area of the object is The time is A-Ih 24 1.81.5)124) 4(1700) t 124.023s -124s

The area of the object is A lh The time is 4m 24 1.8)1.5)24) 4(1700) 1+(9.529x10)r-4.8 9.529x 10-3 ) t 3.8 t 398.78 - 399s The time taken for the object to drop its speed to 11m/s to 5m/s are 124s and 399s