A man in a boat moving at constant speed of 60km/h relative to the shore throws an object in the forward direction with a speed of 30km/h. What is the speed of the object as measured by an observer at rest at the shore?

Assuming the mass of the object is negligible compared to the mass of the person and the boat, then the speed of the object is 30km/h in addition to the speed of the boat.

Using a terrestrial frame of reference, the apparent speed of the object by a stationary observer on the shore is
60+30=90 km/h

To determine the speed of the object as observed by an observer at rest on the shore, we need to consider the concept of relative velocities.

Relative velocity is the velocity of an object in respect to another object. In this case, we have two moving objects – the man in the boat and the object being thrown.

The velocity of the man in the boat is given as 60 km/h relative to the shore, and he throws the object in the forward direction with a speed of 30 km/h.

To find the speed of the object as observed by the shore observer, we need to add the velocities of the man in the boat and the velocity of the thrown object. Since they are both moving in the same direction, we simply add their velocities.

So, the speed of the object as measured by an observer at rest on the shore is

60 km/h (velocity of the man in the boat) + 30 km/h (velocity of the thrown object) = 90 km/h.

Hence, the speed of the object as measured by an observer at rest on the shore is 90 km/h.