For technology project, a student has built a vehicle, of total mass 5 kg, that moves itself. As shown in the figure, it runs on four light wheels. A reel is attached to one of the axles, and a cord o

Question

For technology project, a student has built a vehicle, of total mass 5 kg, that moves itself. As shown in the figure, it runs on four light wheels. A reel is attached to one of the axles, and a cord originally wound on the reel goes up over the pulley attached to the vehicle to support an elevated load. After the vehicle is released from rest, the load descends very slowly, unwinding the cord to turn the axle and make the vehicle move forward. Friction is negligible in pulley and axle bearings. The wheels do not slip on the floor. The reel has been constructed with a conical shape so that load descends at a constant low speed while the vehicle moves horizontally across the floor with a constant acceleration, reaching a final velocity of 3 m/s. Mark the correct option(s) :

Options:(select one or more)

Answer:

A, D

Solution:

Impulse from floor friction = $Δ p = 5 \times 3 = 15$ N·s - (A).

Wheels roll without slipping, so the contact point is instantaneously at rest: friction does no work - (B) wrong.

Energy: the load's PE loss becomes the vehicle's KE: $Δ U = - \frac{1}{2} (5) (3^{2}) = - 22.5$ J, not -27 J - (C) wrong.

The only external horizontal force on the vehicle is ground friction; it causes the acceleration - (D).

TestHub · Accepted Answer

Impulse from floor friction = Δ p = 5 × 3 = 15 N·s - (A). Wheels roll without slipping, so the contact point is instantaneously at rest: friction does no work - (B) wrong. Energy: the load's PE loss becomes the vehicle's KE: Δ U = − 2 1 ​ ( 5 ) ( 3 2 ) = − 22.5 J, not -27 J - (C) wrong. The only external horizontal force on the vehicle is ground friction; it causes the acceleration - (D).

Physics - Center of Mass Question with Solution | TestHub

Options:(select one or more)

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