Question

I had a lab where we had to find the frictional force of a system. A cart was let go at the top of a 15 degree incline and the time it took the cart to reach the bottom of the incline was measured. I need to find the change in energy of the system. The distance is 90cm. The velocity of the cart was 0.517 m/s. The force it took for the cart to go up was 2.08 N and the mass on the hanger was 0.212 kg. The force it took the cart to go down was 1.76 N and the mass on the hanger was 0.180 kg. The equation they gave for the change in energy is 1/2(m_w+m_c)v² - (m_c sin(theta) - m_w)gd. m_w is mass of the weights and m_c is mass of cart. The mass of the cart is 0.256 kg. And the mass of the weights is above. Can you please help me solve for the change in energy and can delta E ever be positive in this experiment? You use the delta E to find the frictional force by using f = - delta E / d.

Answer 1

solution

To find the friction force the following equation is used:

we already have the distance d = 90cm = 0.9m. But we need to find .

To solve we will use the equation proposed in the statement:

where g is gravity,

To determine we will only use the data when the object is going down the ramp.

In this experiment the energy can be positive, since the friction energy should not be large enough to stop the car before traveling 90 cm.

Now that we have we can determine the friction force

if is negative, the force of friction would be positive and would have no physical sense. The force of friction is negative because it opposes the movement of the object.