# Physics circular motion problem, totally stumped.?

Point on a rotating turntable 20.0 cm from the center accelerates from rest to 0.700 m/s in 1.75s. At t=1.25s, find magnitude of the radial acceleration, tangential acceleration and total acceleration.

Update:

Point on a rotating turntable 20.0 cm from the center accelerates uniformly from rest to 0.700 m/s in 1.75s. At t=1.25s, find magnitude of the radial acceleration, tangential acceleration and total acceleration.

Relevance

You forgot to state that it accelerated UNIFORMLY, that is at an unchanging rate. Without that stipulation, the answers would be indeterminate.

O.K. --- So, assuming UNIFORM ANGULAR ACCELERATION, the turntable accelerates to a rotational speed of 0.700 m/s in 1.75s. These figures are nicely adjusted to tell one that the acceleration rate of the (linear) rotational speed is

a = 0.700/1.75m/s^2 = 0.400m/s^2.

Thus the rotational speed at 1.25s will be v = at = 0.500m/s.

Then its INWARDLY DIRECTED radial acceleration, v^2 / r, will be (0.500)^2 / 0.20m/s^2 = 1.25m/s^2.

The tangential acceleration is still a = 0.400m/s^2.

Therefore the TOTAL ACCELERATION is [1.25^2 + 0.4^2]^(1/2)m/s^2 = 1.312...m/s^2. This total acceleration is directed inwards from the "forward tangential direction" at an angle arctan (1.25/0.4) = arctan (3.125) = 72.25... degrees.

Live long and prosper.