Calculate the initial recoil spped of the boat

In summary, the conversation discusses the calculations for the initial recoil speed of a boat after a man throws a 5kg rock out of it at a speed of 20 m/s, and the loss of mechanical energy due to friction. It also mentions the concept of conservation of momentum and the relationship between force of friction and mass. The second part of the conversation involves finding the velocity of a 0.3kg puck after a collision with a 0.2kg puck and calculating the fraction of kinetic energy lost in the collision. Both scenarios involve applying the principles of conservation of momentum and understanding the effects of external forces such as friction on an object's motion.
  • #1
HurricaneH
10
0
1. A 75KG man stands in a 100kg rowboat at rest in still water. He faces the back of the boat and throws a 5kg rock out of the back at a speed of 20 m/s. The boat recoils forward 4.2 m..
Calculate the initial recoil spped of the boat, the loss in mecahnical energy due to friction, the effective coefficient of friction.

Ok, what throws me off is that 4.2 meters that it recoils...


2. A 0.3kg puck, at rest, is struck by a 0.2 kg puck moving along the xaxis with a speed of 2 m/'s. After the collision, the 0.2 kg puck has a speed of 1 m/s at an angle of 53 degrees to the xaxis. Find the velocity of the 0.3kg puck after the collision, find the fraction of KE lost in the collision.

Momentum would be equal before and after right?
 
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  • #2
1. What's the mechanical energy in this case? What's the relation between mechanical energy and external work (friction in this case)? What's the relation between force of friction and mass?

2. Yup, momentum is always conserved.
 
  • #3
HurricaneH said:
1. A 75KG man stands in a 100kg rowboat at rest in still water. He faces the back of the boat and throws a 5kg rock out of the back at a speed of 20 m/s. The boat recoils forward 4.2 m..
Calculate the initial recoil spped of the boat, the loss in mecahnical energy due to friction, the effective coefficient of friction.

Ok, what throws me off is that 4.2 meters that it recoils...


2. A 0.3kg puck, at rest, is struck by a 0.2 kg puck moving along the xaxis with a speed of 2 m/'s. After the collision, the 0.2 kg puck has a speed of 1 m/s at an angle of 53 degrees to the xaxis. Find the velocity of the 0.3kg puck after the collision, find the fraction of KE lost in the collision.

Momentum would be equal before and after right?

1. Remember that there is conservation of momentum to consider. Then you can use that information to calculate the loss of energy too.

2. Same principles :-)
 
  • #4
HurricaneH said:
1. A 75KG man stands in a 100kg rowboat at rest in still water. He faces the back of the boat and throws a 5kg rock out of the back at a speed of 20 m/s. The boat recoils forward 4.2 m..
Calculate the initial recoil spped of the boat, the loss in mecahnical energy due to friction, the effective coefficient of friction.

Ok, what throws me off is that 4.2 meters that it recoils...

Conservation of momentum - a 5kg rock goes one direction, the boat and man conserve momentum by going the opposite direction at a given speed (initial recoil speed). The boat and man decelerate back to zero velocity (how much of a loss in mechanical energy is that). What coefficient of friction decelerates your boat from initial recoil speed to zero in 4.2 meters?
 

FAQ: Calculate the initial recoil spped of the boat

What is the formula for calculating initial recoil speed of a boat?

The formula for calculating initial recoil speed of a boat is: initial recoil speed = (mass of object thrown * velocity of object thrown) / mass of boat.

What is the significance of calculating initial recoil speed of a boat?

Calculating initial recoil speed of a boat helps determine the amount of force exerted on the boat when an object is thrown from it. This information can be useful for designing boats and understanding the impact of objects on boats during water activities.

What units are typically used for measuring initial recoil speed of a boat?

Initial recoil speed of a boat is typically measured in meters per second (m/s) or feet per second (ft/s).

What factors can affect the initial recoil speed of a boat?

The initial recoil speed of a boat can be affected by the mass and velocity of the object being thrown, as well as the mass and design of the boat itself. Other factors such as wind and water conditions may also play a role.

Can the initial recoil speed of a boat be negative?

Yes, the initial recoil speed of a boat can be negative if the object thrown from the boat has a greater mass and velocity than the boat itself. This means that the boat will move in the opposite direction of the thrown object.

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