What is the power input at time t=3s for the force of 5N on an 8kg object?

In summary, the conversation discusses the calculation of velocity and power for a single force acting on an object, as well as determining the power developed by a car's engine and its speed after a certain time. The equations used include F=ma, p=W/t, and 1/2 mv^2.
  • #1
nns91
301
1

Homework Statement



1. A single force of 5N acts in the x direction on a 8kg object. (a) If the object starts from rest at x=0 at time t=-, find its velocity v as a function of time. (b) Write an expression for the power input as a function of time. (c) What is the power input of the force at time t=3s

2.A car manufacturer claims that his car can accelertate from frest to 100 km/h in 8s. The car's mass is 800kg.

(a) Assuming that this performance is achieved at constant power, determine the power developed by the car's engine.
(b) What is the car's speed after 4s (neglect friction and air resistance)

Homework Equations



p=W/t


3. The Attempt at a Solution [/b

1. I could not even do part a of number 1. Can you guys help me ?

2. So since it's constant power P=W/t. W can be calculated by 1/2 mv^2 right ?

How can I do part b ? Do I just use the P from previous calculation and multiply by time 4 s to get W. and set W=1/2 mv^2 ??
 
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  • #2
1a) F = ma gives you the acceleration, use it to find v(t).
1b) With 1a) you can get an expression for the work performed by the force on the object. Relate the work to the power and express p(t).
1c) Use 1b).

2a) You can express the cars kinetic energy at 100 km/h. This energy has been received linearly in time.
2b) You know the kinetic energy given after 4 s from 2a), relate it to velocity.
 
  • #3
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
 
  • #4
nns91 said:
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
Well, it differs in time, but it is given linearly according to the problem description, starting at 0 going up to the maximum value after 8 s. From 2a) you can express energy given per time unit which should give you energy given after 4 s.
 
  • #5
Can I just calculate the acceleration and find velocity from there ?
 
  • #6
Can I just calculate the acceleration and find velocity from there ?
 

1. What is work and energy?

Work and energy are two fundamental concepts in physics. Work is defined as the force applied to an object multiplied by the distance the object travels in the direction of the force. Energy, on the other hand, is the ability of an object to do work. In simpler terms, work is the transfer of energy from one object to another.

2. How is work related to energy?

Work and energy are closely related because work is a measure of the transfer of energy from one object to another. When work is done on an object, energy is transferred to that object, and vice versa, when work is done by an object, energy is transferred from that object to another.

3. What are some common examples of work and energy?

Some common examples of work and energy include lifting objects, pushing or pulling a heavy object, and using machines like a bicycle or a car. In all of these cases, work is being done to transfer energy from one object to another.

4. How is work calculated?

Work is calculated by multiplying the force applied to an object by the distance the object moves in the direction of the force. Mathematically, it can be expressed as W = F x d, where W is work, F is force, and d is distance.

5. What is the difference between potential and kinetic energy?

Potential energy is the energy an object possesses due to its position or state. It is stored energy that can be converted into other forms of energy, such as kinetic energy. Kinetic energy, on the other hand, is the energy an object has due to its motion. It is the energy an object possesses when it is in motion.

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