**About me**** and why I created this physics website.**

A motorcycle traveling on the highway at a speed of 120 km/h passes a car traveling at a speed of 90 km/h. From the point of view of a passenger on the car, what is the velocity of the motorcycle? Answer: 30 km/h

A ball is kicked off the back of a pickup truck traveling at 50 km/h. A pedestrian on the ground sees the ball hit the pavement and then bounce straight up. What was the velocity of the ball relative to the truck?

See answer

A duck swims at a constant speed from one side of a river to the other side in a time of 4 seconds. The river is 6 meters wide and it is flowing at a speed of 2 m/s. What is the velocity of the duck and what is its direction of travel, with respect to ground?

See answer

Why is it easier for an airplane to take off into the wind?

See answer

A car is driving down the road at a velocity

See answer

In a skills competition, a hockey player is skating across the ice at a velocity

See answer

A scotch yoke mechanism is shown in the figure below, with dimensions given in units of meters. The pin is rigidly connected to the crank wheel which is rotating at

See answer

Answer for Problem # 2

You first have to assume that the truck velocity and relative ball velocity are both in the horizontal direction, since no additional information is given. For the ball to bounce straight up, it would need essentially zero horizontal velocity relative to the ground, which means that the velocity of the ball relative to the truck was 50 km/h. Note that this assumes that the ball is not spinning, since spin would cause the ball to deflect sideways after bouncing off the pavement.

Answer for Problem # 3

Since the duck is swimming at constant speed across the river, and with respect to it, its speed is 6/4 = 1.5 m/s with respect to the river. The river is flowing at a speed of 2 m/s (with respect to ground), so the magnitude of the velocity of the duck with respect to ground can be found using the Pythagorean theorem, which is then

Answer for Problem # 4

For an airplane to generate aerodynamic lift, there must be a high enough relative velocity between the wings and the air. If an airplane takes off by traveling into the wind, it does not have to travel as quickly with respect to ground. This in turn means that it can take off over a shorter travel distance over the runway than if there was no wind present.

Answer for Problem # 5

For the newspapers to fly parallel to the driveways when they are airborne, the component of velocity of

Answer for Problem # 6

For the puck to hit the target, it must travel along the line of sight. This means that the component of velocity of

Answer for Problem # 7

This is a tricky problem! You have to recognize that the pin both rotates and translates relative to the slot, which both contribute to the sliding velocity relative to the slot. The pin makes contact with both sides of the slot at the same time, but we only need to consider contact with one side of the slot, so let's choose the right side. Let's also choose a sign convention where up is positive and down is negative. Now, the pin rotates counterclockwise, at an angular velocity of

Return to

Return to