A classmate wanted to use the knowledge of circular motion he had learned to measure the speed of his bicycle. When he was riding on a straight road, he recorded it with a stopwatch In a period of time t, the pedal turns K circles, then Write the expression of the forward speed of the bicycle

A classmate wanted to use the knowledge of circular motion he had learned to measure the speed of his bicycle. When he was riding on a straight road, he recorded it with a stopwatch In a period of time t, the pedal turns K circles, then Write the expression of the forward speed of the bicycle

The diameter D of bicycle wheel should also be measured. The bicycle speed should be equal to the ratio of distance to time. The expression is 2 π KD / T

A starts from a place by bike at the speed of 16km / h and goes along the straight road for 0.5h. B has something urgent to catch up with a, so he starts from the same place by motorcycle at the speed of 36km / h to catch up with a?
(2) What is the distance a has traveled at this time?

1 a 0.5h driving 16 * 0.5 = 8km
B is 20km / h faster than a
So the time needed is 8 / 20 = 0.4h
2 a total of 0.4 + 0.5 = 0.9h
Therefore, a passes through 0.9 * 16 = 14.4km

On a straight road, a travels at a speed of 10m / s by car and B travels at a speed of 5m / s by bicycle
A. When starting from the same point and moving in the same direction at the same time, a observed that B was away from B at a speed of 5m / s. when starting from the same point and moving in the same direction at the same time, B observed that a was close to C at a speed of 5m / s. when starting from the same point and moving in the opposite direction, a observed that B was away from D at a speed of 15m / s. when starting from the same point and moving in the opposite direction, B observed that a was close to C at a speed of 15m / s

A. When moving in the same direction, a observes that B is using a as the reference system, and B is far away at a speed of 5 m / s, so a is correct; B. when moving in the same direction, B observes that a is using B as the reference system, and a is far away at a speed of 5 m / s, so B is wrong; C. when moving in the opposite direction, a observes that B is using a as the reference system, and B is far away at a speed of 15 m / s, so C is correct; D. when moving in the opposite direction, a observes that B is using a as the reference system, and B is far away at a speed of 15 m / S When B observed a, B took B as the reference frame, and a was away at the speed of 15m / s, so D was wrong, so AC was chosen

Party A and Party B ride bicycles from two places 50km apart. The speed of Party A is 15km / h and that of Party B is 10km / h
How long did it take for them to be 25 km apart?

Two cases
Number 1: no meeting
So it takes: (50-25) / (15 + 10) = 1 hour
Second: distance after meeting
So it takes: (25 + 50) / (15 + 10) = 3 hours