Block, Ramp, and Spring

A block of mass m m is positioned on a right-triangular ramp of vertical height h h and mass M M . A spring with force constant k k and natural length L 0 L_0 is attached between the ramp and the wall as shown. All surfaces are smooth. The block can slide along the ramp surface, and the ramp can slide along the floor. The ramp makes an angle θ \theta with respect to the horizontal. There is a downward gravitational acceleration g g .

At time t = 0 t = 0 , the block is at the top of the ramp, and the spring is at its natural length L 0 L_0 . Both the block and the ramp are initially at rest. The block slides down the ramp over time.

The block reaches the floor at time t f t_f . Let L L' be the minimum spring length over the period of time between t = 0 t = 0 and t = t f t = t_f . Enter your answer as the following quantity:

100 ( L + t f ) \large{\lfloor 100 \, ( L' + t_f) \rfloor}

Details and Assumptions:
Here, "m" can mean "meter", or it can refer to the block mass, depending on the context
- ( m , M ) = ( 1 k g , 2 k g ) (m , M) = (1 \, kg, 2 \, kg)
- ( k , L 0 ) = ( 50 N / m , 1 m ) (k , L_0) = (50 \, N/m, 1 \, m)
- ( h , θ ) = ( 2 m , π 6 r a d ) (h , \theta) = (2 \, m, \frac{\pi}{6} \, rad)
- g = 10 m / s 2 g = 10 \, m/s^2
- \lfloor \cdot \rfloor denotes the floor function
- During the period of interest, the block remains fully in contact with the ramp, and the ramp remains fully in contact with the floor.
- The block's size is negligible


The answer is 209.

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1 solution

Harsh Poonia
Feb 26, 2019

Whoa! We’re finally finished. But for those of you (initially including me) who thought this problem is easy and does not need these steps, I finally \text{Whoa! We're finally finished. But for those of you (initially including me) who thought this problem is easy and does not need these steps, I finally}

present to you a WRONG solution which oversimplifies things, and since the spring is quite stiff and motion is short, leads to the RIGHT answer. \text{present to you a WRONG solution which oversimplifies things, and since the spring is quite stiff and motion is short, leads to the RIGHT answer.}

This would probably make you appreciate the rigour of the correct solution. \text{This would probably make you appreciate the rigour of the correct solution.}

Please feel free to ask any doubts in comments. Hope this helps. \text{Please feel free to ask any doubts in comments. Hope this helps.}

@Steven Chase please help with this problem discussion on a David Morin Question.

Harsh Poonia - 1 year, 8 months ago

We cannot use a=gsin30 as the frame is accelerating

Ayan Sharma - 1 year, 6 months ago

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